557 trast medium

by

users

that these agents

can

retain their repu-

tation for safety.

SIR,-We have detected specific circulating secretory IgA in

Department of Radiology,

from patients with gonorrhoea using an enzyme-linked immunosorbent assay with an envelope protein from Neisseria gonorrhaeae as antigen and monospecific antisera to either IgA or secretory piece (Immunodiagnostic Research Laboratory, University of Birmingham). The normal mean serum-IgA detected with the assay was 3.7units/ml (106 men) and 4.1 units/ml (131 women). The corresponding values in 403 patients with acute gonorrhoea were 12.6 units/ml and 13.8 units/ml, respectively. The units depend on the enzyme-antibody conjugate used and are thus arbitrary but in all sera the secretory-piece levels correlated closely with IgA concentrations and poorly with the concentrations of other immunoglobulins. In all groups the ratio of mean secretory-piece concentration and mean IgA concentration was the same. Most of the secretory piece and IgA appear to be present as secretory IgA but there may also be some non-secretory IgA, some free secretory piece, and possibly some attached to other immunoglobulins. The method has not yet been fully calibrated with pure IgA but the results suggest that antigonococcal secretory IgA is present in ng/ml amounts compared with the g/ml amounts of antigonococcal IgG.’I The value of secretory IgA antibody concentrations in the diagnosis of gonorrhoea-which is at least as great as that of IgG concentrations-will be dealt with elsewhere. The question of general immunological and perhaps practical interest is how accurately the concentration of serum-secretory-IgA reflects the local production of secretory IgA antibody from which it presumably derives. Thompson et al. by means of gel diffusing techniques demonstrated secretory IgA in the serum of 41% of patients with untreated adult coeliac disease and in 9% of normal subjects but did not determine the antigenic specificity. Secretory piece has been found linked to IgM in patients deficient in IgA.3 It will combine with IgM but not with IgG.4 serum

City Hospital,

PETER DAVIES

Nottingham NG5 1PD

SOMATOSTATIN-TOLBUTAMIDE TEST IN HYPERINSULINISM

SIR,-Dr Del Arbol and colleagues (Feb. 4, p. 281) have found a complete inhibition by somatostatin of tolbutamideinduced insulin secretion in a patient with hyperinsulinism due to pancreatic beta-cell hyperplasia. This effect of somatostatin on the insulin response to tolbutamide is also seen in normal subjects.’ In contrast, an absence of inhibition by somatostatin has been reported in four patients with insulin-producing tumours. Lorenzi et a1.2 suggested a possible role for somatostatin in the diagnosis of insulinoma. Suppression of insulin response to tolbutamide may also be found, however, in true beta-cell adenoma. In one patient with a well-differentiated insulinoma, infusion of somatostatin (500 g in 50 ml saline over one hour) completely blocked the release of insulin after tolbutamide stimulation (1000 mg given as a bolus intravenously 30 min after the start of the infusion).3 The sensitivity to somatostatin is thus not consistently lost in beta-adenoma cells. A somatostatin-tolbutamide test should be done in cases of (suspected) hyperinsulinism because more data are needed. However, it seems unlikely that the test will differentiate uniformly between normal beta-cell function and insulinoma or between islet-cell hyperplasia and neoplasia. Department of Internal Medicine, Deaconess Hospital, Hilversum, Netherlands

F. VAN KERSEN

VASOPRESSIN AND MEMORY

SIR,-Dr Legros and his colleagues (Jan. 7,

p.

41) reported

improved learning and memory performances in a group of elderly men after daily administration of 16 i.u. of lysine-8vasopressin for 3 days in controlled studies with a placebo group. No significant changes were noted in clinical or biochemical data after vasopressin or placebo. But psychometric tests revealed significant differences between the two groups after treatment. The improvement in the vasopressin group could have been due to the effects of vasopressin or practice in the use of the psychological tests. Repeated administration of memory tests generally improves performance.4.5 How much can vasopressin improve performance beyond the improvement due to practice? The placebo (control) group’s performance got worse (instead of getting better or staying the same, as predicted) on many of the repeat tests. Worse performances for the placebo group and improved performances for the vasopressin group could result in significant differences. In view of the small number of patients used in the trial and the lack of biochemical changes in the vasopressin group, perhaps another placebo group should be run to evaluate the reliabilty of the findings before it is concluded that vasopressin alters attention, concentration, and short-term memory. Mental Performance and Aging Laboratory, Geriatric Research, Educational and Clinical Center, Veterans Administration Outpatient Clinic, Boston, Massachusetts 02108, U.S.A. 1. Gerich,

LEONARD W. POON

J. E., Lorenzi, M., Schneider, V., Forsham, Metab. 1974, 39, 1057. 2. Lorenzi, M., Gerich, J. E., Karam, J. H., Forsham, 1121. 3. Van Kersen, F. Nerh. J. Med. 1976, 19, 5. 4. Lehman, H. E., Kral, V. A. Geriatrics, 1968, 5. Murrell, F. H. J. Geront. 1970, 25, 268.

ANTIGONOCOCCAL IgA IN GONORRHŒA

2,

142.

P. H.

J.

clin. Endocr.

P. H. ibid. 1975, 40,

Department of Bacteriology, Wright-Fleming Institute, St. Mary’s Hospital Medical School, London W2 1PG

A. A. GLYNN

C. ISON

BIDIRECTIONAL MIXED LYMPHOCYTE REACTION IN FETAL/MATERNAL PAIRS

SIR,-Finn et al. claimed that their findings of a relatively low mixed lymphocyte reactivity (M.L.R.) in fetal/maternal pairs indicated tolerance between maternal and fetal cells and that this must be due largely to a genetic mechanism. The basic data as presented are suspect in that M.L.R. results were given as stimulation indices (s.l.) (mean count of mixed lymphocyte cultures divided by mean count of unstimulated cells). Small variations in the rate of D.N.A. synthesis by unstimulated cells will result in large alterations in s.i. Since fetal cells frequently show a high level of spontaneous 3H-thymidine incorporation,6 low s.i.s might be expected if these are computed from the formula (c.p.m. M+F) — (c.p.m. F) where M and F are maternal and fetal cells respectively. What denominator did Finn et al. use-c.p.m. M, c.p.m. F, or -1c.p.m. M+ c.p.m. F? We and others7.8 consider that M.L.R. data should be presented as (c.p.m. in stimulated cultures)-(c.p.m. in unstimulated cultures)-i.e., as incremental or net stimulation. 1. Glynn, A. A., Ison, C. Br. J. vener. Dis. 1978, 54, 97. 2. Thompson, R. A., Asquith, P., Cook, W. T. Lancet, 1969, ii, 517. 3. Thompson, R. A. Nature (Land), 1970, 226, 946. 4. Mach, J. P. Nature (Land) 1970, 228, 1278. 5. Finn, R., St. Hill, C. A., Davis, J. C., Hipkin, L. J., Harvey, M. Lancet, 1977, ii, 1200. 6. Andersen, V., Andersen, E. Acta pædiat. scand. 1974, 63, 266. 7. Herva, E. Lancet, 1976, i, 919. 8. Bondevik, H., Helgesen, A., Thoresen, A. B., Thorsby, E. Tissue Antigens,

1974, 4, 268.

Antigonococcal IgA in gonorrhoea.

557 trast medium by users that these agents can retain their repu- tation for safety. SIR,-We have detected specific circulating secretory IgA...
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