OF CLINICAL MICROBIOLOGY, Jan. 1992, p. 126-131 0095-1137/92/010126-06$02.00/0 Copyright C) 1992, American Society for Microbiology

JOURNAL

Vol. 30, No. 1

Comparison of Antibody Reactivity to Human Immunodeficiency Virus Type 1 (HIV-1) gpl60 Epitopes in Sera from HIV-1-Infected Individuals from Tanzania and from the United States RONALD Q. WARREN,1'2 WATOKY M. M. M. NKYA,3 JOHN F. SHAO,4 STEPHANIE A. ANDERSON,1'2 HANS WOLF,1 CRAIG W. HENDRIX,2'5 PATRICK KANDA,"2 MEL WABUKE,6 R. NEAL BOSWELL,2'5 ROBERT R. REDFIELD,7 AND RONALD C. KENNEDY'.2* Department of Virology and Immunologyl* and Center for AIDS Research,2 Southwest Foundation for Biomedical Research, San Antonio, Texas 78284; Kilimanjaro Christian Medical Center, Moshi,3 and Muhimbili Medical Center, Dar es Salaam,4 Tanzania; Department of Medicine, Wilford Hall Medical Center, Lackland Air Force Base, Texas 782365; Baxter Healthcare Corp., Duarte, California 910106; and Department of Retroviral Research, Walter Reed Army Institute of Research, Rockville, Maryland 208507 Received

5

August 1991/Accepted 14 October 1991

In this study, we compared sera from 159 human immunodeficiency virus type 1 (HIV-1)-infected individuals from Tanzania and 103 infected individuals from the United States for antibodies reactive with 10 HIV-1 gpl60 epitopes defined by synthetic peptides. Our data indicate that the anti-gpl60 antibody fine specificity differs between infected individuals from these two geographically diverse populations. For example, 50% of the Tanzanian sera contained antibodies reactive with an immunodominant HIV-1 gp4l epitope defined by peptide 600-611, whereas 91% of the sera from the United States were reactive. Differences in serologic reactivity between HIV-1-infected individuals from Tanzania and the United States were also observed with gpl60 epitopes defined by peptides 503-528 and 846-860. Included among the peptides examined were four which corresponded to the V3 region of gp120. The majority of sera from either country contained antibodies reactive with peptide RP142, whose V3 sequence is based upon that of HIV-1 isolate MN. Further characterization of serologic reactivity suggested that sera from Tanzania were more likely to neutralize HIV-1 isolate IIIB or MN in vitro than were sera from the United States. These differences in antibody fine specificity between HIV-1-infected individuals from Tanzania and the United States suggest that regional isolates of HIV-1 may exist.

Two major epidemiologic patterns of human immunodeficiency virus type 1 (HIV-1) infection have been observed worldwide (1, 3, 4, 19, 20). Pattern I is present in the United States and Europe and afflicts mainly homosexual males and intravenous drug abusers. Pattern II is found predominantly in Africa and is characterized by the heterosexual spread of HIV-1. The male/female infectivity ratios have been reported to be approximately 1:1 in Africa and closer to 10:1 in the United States (16). Factors that may contribute to these epidemiologic patterns include (i) a higher incidence of male homosexuality and intravenous drug abuse in the United States and Europe; (ii) a higher incidence of sexually transmitted diseases in Africa; (iii) endemic malaria and tuberculosis infections in Africa; and (iv) the presence of regional HIV-1 isolates that may differ in levels of virulence. HIV-1 infection represents a serious health threat to many nations in Africa. Recent surveys in Tanzania have indicated a seroprevalence rate of 4%, with 4,100 cases of AIDS being reported as of January 1990 (26, 32). While the clinical and immunological profiles of HIV-1-infected individuals in the United States and Europe have been well characterized, information concerning HIV-1 infection in Africa is far less complete. The collection of immunological data from infected individuals, as well as the sequencing of African HIV-1 isolates, will be necessary to better understand geographic differences in HIV-1 infections. Information of this type will also be useful in the design of more effective AIDS diagnostic and therapeutic products worldwide.

In this report, we examined sera from HIV-1-infected individuals from both Tanzania and the United States for antibodies reactive with 10 selected HIV-1 gpi60 epitopes defined by synthetic peptides. These included four peptides whose sequences were based on the principal neutralizing determinant (PND) of gp120. Sera were also tested for the ability to neutralize divergent HIV-1 isolates in vitro. Our data suggest that significant differences in antibody fine specificity exist between HIV-1-infected individuals from Tanzania and the United States.

MATERIALS AND METHODS Human sera. Sera from 159 HIV-1-infected individuals from Tanzania and 103 infected individuals from the United States were examined. All sera from HIV-1-infected individuals were confirmed to contain anti-HIV-1 gpi60 antibodies by Western blot (immunoblot) analysis and to demonstrate serologic reactivity to gpl60 by an enzyme-linked immunosorbent assay (ELISA). The HIV-1-infected individuals were grouped as symptomatic or asymptomatic. Symptomatic individuals from both countries presented with weight loss, skin lesions, and/or opportunistic infections. The HIV1-infected individuals from Tanzania comprised 21 males and 138 females, with a mean age of 29.9 years. Among the Tanzanian individuals tested were 55 asymptomatic female prostitutes. All Tanzanian sera examined in this study were found negative for HIV-2 antibodies by Western blot analysis (Ortho Diagnostic Systems Inc., Raritan, N.J.). Sera from the United States were obtained from U.S. military personnel consisting of 102 males and 1 female, with a mean

* Corresponding author. 126

Ab TO gpl6O EPITOPES IN HIV-1-INFECTED INDIVIDUALS

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127

TABLE 1. Amino acid sequences of gp160 synthetic peptides Peptide

425-448 503-528 600-611 616-632 735-752 846-860

304-321b RP135 (308-331)b RP142 (306-330)b RP145 (303-325)b

iVsolat IIIB IIIB IIIB IIIB IIIB IIIB IIIB IIIB MN HAN/SC

Amino acid sequence"

CRIKQIINMWOEVGKAMYAPPISG (CGY)VAPTKAKRRVVQREKRAVGIGALELG LGIWGCSGKLIC

(C)PWNASWSNKSLEQIWNN(G) (Y)DRPEGIEEEGGERDRDRS(GC) (CAY)AIRHIPRRIROGLER(G) (CGY)TRPNNNThKSIRIQRUGP

NNTRKSIRIQRGPGRAFVTIGKIG(C) YNKRKRIHI9PGRAFYTTKNII£( C) NNTRKGIHIGPGRA/FYATGDIIG(C)

" Underlined amino acids represent those which were conserved (>80%). compared with amino acid sequences for 19 other HIV-1 isolates (see Materials and Methods). Amino acids in parentheses were added to facilitate coupling to carrier proteins for related immunization studies. b V3 region of gpl20.

age of 29.8 years. Sera from 10 healthy, uninfected individuals were used as controls. Synthetic gpl60 peptides. Amino acid sequences for synthetic peptides 304-321, 425-448, 503-528, 600-611, 616-632, 735-752, and 846-860 were based upon those of the human T-cell lymphotropic virus type III BH10 isolate (23), and the peptides were synthesized and purified as previously described (29). Peptides RP135, RP142, and RP145, which correspond to the gpl20 V3 regions of HIV-1 isolates IIIB, MN, and composite HAN/SC, respectively, were generously provided by Scott Putney (Repligen, Cambridge, Mass.). Peptide 304-321 corresponds to the amino portion of the V3 loop, while peptides RP135, RP142, and RP145 correspond to more central portions of the V3 loop. The amino acid sequences for all the peptides examined in this study and the degree of sequence conservation for each gp160 epitope are listed in Table 1. For the determination of amino acid sequence homology, the peptide sequences were compared with the corresponding sequences of HIV-1 isolates BRU, HXB2, MN, BRVA, SC, JH3, CDC4, OYI, SF2, HAN, JFL, WMJ2, VRF, ELI, Z2, NDK, JY1, MAL, and Z321 (13). Determination of antibody binding to synthetic peptides by an ELISA. The methods used for detecting antibody reactivity with HIV-1 gpl60 synthetic peptides have been described in detail elsewhere (2, 11). In brief, synthetic peptides were allowed to adhere to microtiter wells overnight at a concentration of 250 ng per well. Fifty microliters of a 1:50 dilution of human sera was reacted in duplicate with each peptide for 1 h at 37°C; this step was followed by washing and the addition of 50 ,ul of peroxidase-conjugated goat anti-human immunoglobulin (Cappel, West Chester, Pa.). After an additional 1 h of incubation and washing, the substrate, 2,2'-

azino-bis(3-ethylbenzthiazoline-6-sulfonicacid)(SigmaChemical Co., St. Louis, Mo.) (0.0005 M) containing 0.05% hydrogen peroxide (Baker Chemical Co., Phillipsburg, N.J.), was added. The optical density (OD) at 410 nm was determined with an MR 600 Microplate Reader (Dynatech Laboratories, Alexandria, Va.). All antisera were screened for reactive antibodies in at least three separate ELISA determinations. Ten HIV-seronegative normal control serum samples were similarly tested for antibodies reactive with the synthetic peptides. Experimental serum OD values greater than three times the mean of the 10 control serum samples were considered positive in reactivity with a given peptide. This positive reactivity cutoff value for these sera exceeded the 95% confidence level. In instances in which the

normal control sera had a negligible OD value and a cutoff value for positive reactivity could not be calculated, an OD value of 0.1 was used as the positive cutoff. Neutralization assay. Two neutralization assays were used in this study. First, a cytotoxicity assay with a dye uptake step to determine cell viability was used to assess the in vitro neutralizing activity of sera against isolate IIIB. Test sera (1:50 dilution) were preincubated at room temperature for 1 h with 100 50% tissue culture infective doses of HIV-1 IIIB. This mixture (25 ,ul) was added to microtiter wells containing 25,000 SupTl cells (50-,lI final volume). The cells were incubated at 37°C for 8 days and fed with 10% fetal bovine serum-RPMI medium on days 3 and 6. On day 8, 10 pul of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (thiazolyl blue) (0.012 M) (Sigma) was added to the wells, and the mixture was incubated for 4 h at 37°C. The cultures were inactivated by the addition of 175 pul of 0.04 N HCl in isopropanol, and the OD was determined at 570 nm. Sera were considered to neutralize HIV-1 IIIB when more than 50% of the SupTI cells remained viable, in comparison with the results in wells containing either normal serum or no virus. This assay has been described in detail elsewhere (24). In the second assay, a p24 antigen capture ELISA was used to determine the neutralizing activity of sera against isolate MN (Retrovirology Coulter Corp., Hialeah, Fla.). This method was used because isolate MN, which readily infects SupTl target cells, did not result in substantial cell death. This assay was performed as described for the IIIB isolate, with the HIV-1 p24 levels being determined in accordance with the manufacturer's recommended procedure for the p24 ELISA. Sera were considered to neutralize isolate MN at a 1:50 dilution when a greater than 50% reduction in p24 levels was detected, in comparison with the results in wells containing either normal serum or no virus. Statistical analysis. A statistical analysis comparing antibody reactivity with the gpl60 epitopes of sera from HIV-1infected individuals from Tanzania and from the United States was performed with the chi-square method (5). The numbers of positive sera from each country were compared for statistical significance. RESULTS The antibody fine specificity for gpl60 epitopes in sera from HIV-i-infected individuals from the United States and Tanzania was examined and compared by an ELISA. This comparison was performed to determine whether differences

128

WARREN ET AL.

J. CLIN. MICROBIOL. gpl 60

of all sera examined contained antibodies reactive with these peptides. This low level of antibody reactivity suggests that gpl60 epitopes defined by peptides 425-448, 616-632, 5%

846-K

PND 425-448 503-528 616-632

mm

303-338

600-611

and 735-752

73.5-752

1

gP41

FIG. 1. Linear map of the gpl60 epitopes used in this study.

existed in the humoral immune response to the envelope HIV-1 between these two geographically div populations. The HIV-1 gpl60 epitopes examined in tlhis study shown in Table 1. The spatial locations of these epitopes gpl60 are shown in Fig. 1. The antibody react from HIV-1-infected individuals with the pan based synthetic peptides is shown in Table 2. Peptide 600-611, which was reactive with 91% (94 of 103 ) of the U.S. sera, was recognized by only 50% (80 of 159) f the Tanza nian sera. The low level of reactivity among th fe Tanzanian sera was surprising, since the gp41 epitope is highly conserved and immunodominant among known HI [V- isolates from the United States. This lower percenttage of sera reactive with peptide 600-611 represented a si gnificant decline (P < 0.001) in comparison with the reactiivity of U.S. sera. Other differences were also observed with two peptides that define carboxyl-terminal epitopes on gpl 20 and gp4ti Approximately half (53%; 85 of 159) of the Ta.nzanian sera contained antibodies reactive with peptide 503-5528. This was a significantly higher percentage (P < 0.05) t]han that observed with the U.S. sera (39%; 40 of 103). We atlso observed that a significantly higher percentage (P < 0.05) iof sera from infected individuals from Tanzania (26%; 41 of 159) than from the United States (12%; 12 of 103) containced antibodies reactive with peptide 846-860. The epitope defined by peptide 425-448 corressponds to the putative CD4 binding site on gpl20. This grp120 epitope appears to be immunorecessive, being reactive)with only 6% (9 of 159) and 3% (3 of 103) of sera from HI [V-1-infected individuals from Tanzania and the United Stu ates, respectively. Two additional HIV-1 gpl60 epitopes , defined by peptides 616-632 and 735-752, also appeared Ito be poorly immunogenic in HIV-1-infected individuals froim both Tanzania and the United States. We observed thait fewer than

of

erse

are

on

elvity

sera

of

are

poorly immunogenic.

Sera from HIV-1-infected individuals from both Tanzania and the United States were also grouped by clinical status (asymptomatic versus symptomatic) to determine whether differences in antibody fine specificity may be associated with disease progression (Table 2). We observed a lower percentage of sera containing antibodies reactive with peptide 425-448 in symptomatic than in asymptomatic individuals from both the United States and Tanzania. None of the sera from symptomatic individuals from either country contained antibodies reactive with peptide 425-448, suggesting that antibodies reactive with this epitope may be lost during disease progression. However, this decrease was not statistically significant, and caution must be used in interpreting antibody reactivity with weakly immunogenic epitopes. We also observed a lower percentage of sera containing antibodies to peptides 503-528 and 846-860 in symptomatic than in asymptomatic individuals from the United States, but not

Antibody reactivity with three other gp160 peptides (peptides 600-611, 616-632, and 735-752) was not markedly different between asymptomatic and symptomatic

from Tanzania.

individuals.

In the next set of experiments, we compared the reactivity of representative serum samples from the United States and Tanzania with four synthetic peptides corresponding to the V3 region of HIV-1 gpi2O (Table 3). The V3 region represents the PND of gp120. Antibodies reactive with this region have been reported to exhibit type-specific activity in both HIV-1-infected humans and HIV-1-infected chimpanzees (9, 12, 27). Peptide 304-321, which corresponds to the amino portion of the V3 loop of isolate IIIB, was reactive with 13 of

68 (19%) and 5 of 39 (13%) serum samples from Tanzania and the United States, respectively. A higher percentage of serum samples from the United States was reactive with the IIIB-based peptide RP135 (12 of 39; 31%), which contains amino acids corresponding to the central region of the V3 loop. Peptide RP142, whose sequence is based upon that of isolate MN, was reactive with the majority of the serum samples examined. Forty seven of 68 (69%) serum samples from Tanzania and 30 of 38 (79%) serum samples from the United States contained antibodies reactive with peptide

TABLE 2. Reactivity of serum samples from HIV-1-infected individuals from Tanzania and the United States with gpl60 epitopes defined by synthetic peptides No.

Source of serum samples

(n)

425-448

(%) of serum samples positive for the following gpl60 epitope:

503-528

600-611

616-632

735-752

846-860

Tanzania

Asymptomatic (131) Symptomatic (28)

9 (7) 0 (0)

69 (53) 16 (57)

65 (50) 15 (54)

1 (1) 0 (0)

4 (3) 1 (4)

34 (26) 7 (25)

Total (159)

9 (6)

85 (53)

80 (50)

1 (1)

5 (4)

41 (26)

3 (5) 0 (0)

35 (43) 5 (23)

74 (91) 20 (91)

2 (3) 1 (5)

3 (4) 0 (0)

12 (15) 0 (0)

94 (91)"

3 (3)

3 (3)

12 (12)"

United States Asymptomatic (81) Symptomatic (22)

40 (39)" 3 (3) Total (103) " Significantly different from Tanzanian serum samples (P < 0.05). " Significantly different from Tanzanian serum samples (P < 0.001).

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Ab TO gpl60 EPITOPES IN HIV-1-INFECTED INDIVIDUALS

TABLE 3. Reactivity of serum samples from HIV-1-infected individuals with peptides corresponding to the V3 region of gpl20 Source of serum samples

Tanzania Asymptomatic Symptomatic Total

6/44 (14) 7/24 (29)

13/68 (19)

United States Asymptomatic Symptomatic Total

RP135

RP142

10/44 (23) 4/24 (17)

RP145

32/44 (73) 15/24 (63)

14/68 (21)

47/68 (69)

38/68 (56)

4/27 (15) 1/12 (8)

10/27 (37) 2/12 (17)

21/27 (78) 9/11 (82)

14/27 (52) 3/13 (25)

5/39 (13)

12/39 (31)

30/38 (79)

17/40 (43)

TABLE 4. Number of distinct V3 region peptides recognized by serum samples from HIV-1-infected individuals

Tanzania Asymptomatic (30) Symptomatic (16) Total (46)

United States Asymptomatic (27) Symptomatic (12)

Source of serum samples (n)

Neutralizing HIV-1 isolate:

Containing antibodies reactive with PND-based

peptide": Tanzania (15) United States (15)

IIIB

MN

RP135

RP142

12 (80) 8 (53)

7 (47) 2 (13)

6 (40) 6 (40)

14 (93) 14 (93)

' See Table 1 for details regarding the peptides.

RP142, indicating the high prevalence of isolate MN or related HIV-1 isolates worldwide. Peptide RP145 represents a hybrid V3 peptide which corresponds to a combination of HIV-1 HAN and SC V3 sequences. We observed that 56 and 43% of serum samples from Tanzania and the United States, respectively, contained antibodies reactive with this peptide. Serum samples from HIV-1-infected individuals were examined for reactivity with multiple PND-based peptides to determine whether the number of peptides recognized differed between asymptomatic and symptomatic individuals (Table 4). We observed that 14 of 27 (52%) serum samples from asymptomatic individuals from the United States recognized two or more PND-based peptides, in contrast to only 3 of 12 (25%) serum samples from symptomatic individuals. With serum samples from the United States, a trend was observed in which a higher percentage of serum samples from asymptomatic individuals than of serum samples from symptomatic individuals contained antibodies reactive with multiple PND-based peptides. This result could reflect the relatively small number of serum samples that were examined. However, no difference in the number of PND-based peptides recognized by serum samples from asymptomatic

Source of serum samples (n)

No. of serum samples (%)

25/44 (57) 13/24 (54)

a See Table 1 for details regarding the peptides.

Total (39)

TABLE 5. Comparison of serum neutralization of HIV-1 IIIB and MN and reactivity with homologous PND-based peptides

No. of serum samples positive/no. of serum samples examined (% positive) for the following V3 peptide":

304-321

129

No. (%) of serum samples recognizing the following no. of V3 region peptides": 4

3

2

1

0

0 (0) 0 (0)

6 (20) 4 (25)

10 (33) 5 (31)

8 (27) 2 (13)

6 (20) 5 (31)

0 (0)

10 (21)

15 (33)

10 (22)

11 (24)

3 (11) 0 (0)

6 (22) 2 (17)

5 (19) 1 (8)

9 (33) 7 (58)

4 (15) 2 (17)

3 (8)

8 (21)

6 (15)

16 (41)

6 (15)

" The V3 region peptides examined for antibody reactivity included IIIBbased 304-321 and RP135, MN-based RP142. and HAN/SC-based RP145.

versus symptomatic individuals from Tanzania was detected. Fifteen representative serum samples each from Tanzania and the United States were also examined for their ability to neutralize HIV-1 isolates IIIB and/or MN in vitro (Table 5). We were interested in determining whether differences exist in the ability of serum samples from these two countries to neutralize HIV-1 isolates in vitro. Twelve (80%) and 8 (53%) of the 15 Tanzanian and 15 U.S. serum samples examined neutralized isolate IIIB. Similarly, 7 (47%) and 2 (13%) of the 15 Tanzanian and 15 U.S. serum samples neutralized isolate MN. For the individuals examined, a higher percentage of Tanzanian serum samples than of U.S. serum samples contained HIV-1-neutralizing antibodies. Interestingly, a high percentage of these 30 serum samples that were examined for neutralizing activity contained antibodies reactive with RP142 (93% of both Tanzanian and U.S. serum samples), yet only 47% of the Tanzanian and 13% of the U.S. serum samples neutralized isolate MN in vitro (Table 5).

DISCUSSION This report examines potential differences in the humoral immune response to selected HIV-1 gp160 epitopes defined by synthetic peptides in the sera of HIV-1-infected individuals from Tanzania and the United States. Specifically, we found that several statistically significant differences in antigpl60 antibody fine specificity existed between infected individuals from these two countries. The greatest difference detected in our study centered on the epitope corresponding to amino acids 600 to 611. This highly conserved viral epitope was recognized by 50% of sera from HIV-1-infected Tanzanians, while 91% of U.S. sera contained reactive antibodies. Previously published data agree well with our data, which indicate that most sera from infected individuals from the United States contain antibodies reactive with peptide 600-611 (7, 8, 14). A similar study of sera from HIV-1-infected individuals from Zaire reported that 71% contained antibodies reactive with peptide 600-611 (6). Together, these data suggest that a lower percentage of sera from African AIDS patients than of sera from U.S. AIDS patients contains antibodies reactive with peptide 600-611. This suggestion may potentially reflect infection by HIV-1 isolates that exhibit diverse amino acid sequences in this region compared with previously characterized HIV-1 isolates. In addition, we found that a significantly lower percentage of U.S. sera than of Tanzanian sera contained antibodies reactive with peptides 503-528 and 846-860. Different antibody responses to HIV-1 viral epitopes suggest that amino acid sequences of some Tanzanian HIV-1 isolates may differ at or near these sites from those of some U.S.

130

WARREN ET AL.

HIV-1 isolates. No difference was observed in serologic reactivity when three weakly immunogenic epitopes (peptides 425-448, 616-632, and 735-752) were examined. Sera were grouped by clinical status (asymptomatic versus symptomatic) to examine whether changes in antibody fine specificity could be detected with disease progression. A lower percentage of sera containing antibodies to peptide 425-448 was observed in symptomatic individuals from both the United States and Tanzania. Sera from symptomatic U.S. individuals were also less likely to contain antibodies to peptides 503-528, 735-752, and 846-860 than were sera from asymptomatic U.S. individuals. While interpreting patterns of antibody binding to weakly immunogenic epitopes (i.e., peptides 425-448, 735-752, and 846-860) is difficult, these results suggest that individuals may lose antibodies to particular gp160 epitopes as the clinical signs of AIDS appear. By comparing antibody specificities of healthy and symptomatic patients, the impact of antibodies to specific HIV-1 epitopes on disease progression may be better understood. Previous studies have suggested that the capacity of the immune system to mount a broadly reactive antibody response to HIV-1 may decline with disease progression (15, 18, 30, 31). The reduction in antibody reactivity with gp160 epitopes observed in our study could potentially result in the loss of beneficial antiviral antibodies and may lead to an accelerated rate of disease progression. Antibody reactivity with four peptides corresponding to the PND (V3 region of gp120) of HIV-1 was also examined. A number of studies have indicated that antibodies reactive with this epitope demonstrate type-specific neutralizing activity in vitro and may exert a beneficial effect in vivo (10, 12, 21, 25, 27, 28). The examination of sera for antibody reactivity with PND-derived peptides can also be useful in estimating the prevalence of HIV-1 isolates or related viral families within particular geographic areas. Two PND-derived peptides (304-321 and RP135), whose sequences were based upon those of isolate IIIB, were reactive with fewer than one-third of sera from either the United States or Tanzania. Peptide RP135 was reactive with a higher percentage of sera than was peptide 304-321. This result suggests that peptide RP135, which represents the central portion of the V3 loop, may represent a more immunodominant epitope(s) than peptide 304-321. In addition, we observed that greater than 65% of sera from both the United States and Tanzania contained antibodies reactive with peptide RP142. The sequence of this peptide is analogous to that of the V3 region of isolate MN. This high level of antibody reactivity suggests that isolate MN or antigenically related isolates are commonly found in both countries. This suggestion agrees with a previous report indicating the widespread prevalence of isolate MN in the United States (12). Peptide RP145, a hybrid V3 peptide, was reactive with approximately one-half of the Tanzanian and U.S. sera tested. An interesting observation was that sera from asymptomatic individuals from the United States frequently contained antibodies reactive with more PND-based peptides than did sera from symptomatic individuals. Specifically, 52% of sera from asymptomatic individuals contained antibodies reactive with two or more of the PND-based peptides examined, while only 25% of sera from symptomatic individuals did so. No difference was observed in reactivity with the four PND-based peptides examined between the asymptomatic and symptomatic individuals from Tanzania. This trend observed in sera from HIV-1-infected individuals from the United States could have resulted from the small number of sera examined. Alternatively, the presence in sera of

J. CLIN. MICROBIOL.

antibodies which react with multiple PND-based peptides could correlate with a better clinical status. The PND of gpl20 currently represents a prime target for potential AIDS vaccines (22). Thus, it is critical to determine whether the detection of anti-PND antibodies in sera correlates with the neutralization of HIV-1 in vitro. The results presented indicate that no strong correlation exists between the presence of anti-PND antibodies in sera from HIV-1infected individuals and the ability to neutralize homologous HIV-1 isolates in vitro. These results point out the importance of neutralizing epitopes which lie outside the PND (reviewed in reference 17). However, the peptides used in this study are predominantly detected by antibodies against linear or continuous epitopes, especially in an ELISA format. The possibility exists that antibodies which neutralize HIV-1 in vitro may recognize conformational or discontinuous epitopes associated with the PND. The serologic data in this study suggest that the fine specificity of antibodies directed against selected HIV-1 gpl60 epitopes differs between infected individuals from Tanzania and the United States. These different patterns of antibody fine specificity may be partially due to the presence of regional HIV-1 isolates which differ in envelope amino acid sequences. The high level of sequence variability found among gpl60 envelope glycoproteins (13) may lead to the presence of geographically distinct HIV-1 isolates. ACKNOWLEDGMENTS This work was supported by grants A126462, A125151, and A128696 from the National Institutes of Health, by a contract from the U.S. Army Research and Development Command, and by the U.S. Agency for International Development. We thank Claire Nypaver for technical assistance. REFERENCES 1. Centers for Disease Control. 1986. Update: acquired immunodeficiency syndrome-Europe. Morbid. Mortal. Weekly Rep. 35: 35-46. 2. Chanh, T. C., G. R. Dreesman, P. Kanda, G. P. Linette, J. T. Sparrow, D. D. Ho, and R. C. Kennedy. 1986. Induction of anti-HIV neutralizing antibodies by synthetic peptides. EMBO J. 5:3065-3071. 3. Curran, J. W. 1985. The epidemiology and prevention of the acquired immunodeficiency syndrome. Ann. Intern. Med. 103:

657-662. 4. Curran, J. W., W. M. Morgan, A. M. Hardy, H. W. Jaffe, W. W. Darrow, and W. R. Dowdle. 1985. The epidemiology of AIDS: current status and future prospects. Science 229:13521357. 5. Downie, N. M., and R. W. Heath. 1965. Basic statistical methods, 2nd ed., p. 160-175. Harper & Row, New York. 6. Gnann, J. W., Jr., J. B. McCormick, S. Mitchell, J. A. Nelson, and M. B. A. Oldstone. 1987. Synthetic peptide immunoassay distinguishes HIV type 1 and HIV type 2 infections. Science

237:1346-1349. 7. Gnann, J. W., Jr., J. A. Nelson, and M. B. A. Oldstone. 1987. Fine mapping of an immunodominant domain in the transmembrane glycoprotein of human immunodeficiency virus. J. Virol. 61:2639-2641. 8. Gnann, J. W., Jr., P. L. Schwimmbeck, J. A. Nelson, A. B. Truax, and M. B. A. Oldstone. 1987. Diagnosis of AIDS by using a 12-amino acid peptide representing an immunodominant epitope of the human immunodeficiency virus. J. Infect. Dis. 156:261-267. 9. Goudsmit, J., C. Debouck, R. H. Meloen, L. Smit, M. Bakker, D. M. Asher, A. V. Wolff, C. J. Gibbs, Jr., and D. C. Gajdusek. 1988. Human immunodeficiency virus type 1 neutralization epitope with conserved architecture elicits early type-specific antibodies in experimentally infected chimpanzees. Proc. Natl.

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Comparison of antibody reactivity to human immunodeficiency virus type 1 (HIV-1) gp160 epitopes in sera from HIV-1-infected individuals from Tanzania and from the United States.

In this study, we compared sera from 159 human immunodeficiency virus type 1 (HIV-1)-infected individuals from Tanzania and 103 infected individuals f...
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