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348 8 McGarry, R. C., Helfand, S. L., Quarles, R. H. a at (1983) Nature (London) 306, 376-378 9 Benczur, M., Petrlfnyi, C. G., PAlffy, G. etal. (1980) Clin. Exp. lmmunoL 39, 657-662 10 Neighbour, P. A., Grayzel, A. I. and Miller, A. E. (1982) Clin. Exp. lmmunol. 49, 11-21 11 MeFarlin, D. E. and McFarland, H. F. (1982) New EnglandJ. Med. 307, 1183-1188; 1246-1251 12 Antel, J. P., ed. (1983) NeurologgeClini~xvol. I, no. 2, W. B. Saunders CO., Philadelphia 13 Waksman, B. H. and Reynolds, W. E. (1984) Proc. Soc. Exp. Biol. Med. 175, 282-294 14 Sato, S., Quarles, R. H. and Brady, R. O. (1982)J. Neuroehem. 39, 97-105 15 Kuwert, E. and Bertrans, J. (1972) Eur. Neurol. 7, 65 16 Weiner, H, L. and 8ehocket, A. L. (1979) Neurolog~29, 1504-1508 17 Tsokamoto, T., Ebina, T., Takase, S. etal. (1982) TohokuJ. Exp. Med. 136, 121-128 18 Dore-Duffy, P. and Zurier, R. B. (1981) Clin. Immunol. Inmmnopath. 19, 303-313 19 Merrill, J. E., Gerner, R. H., Myers, L. W. eta/. (1983) J. Neuroimmunol. 4, 223-237; 239-251 20 Oger, J. J-F., Szuchet, S., Antel, j. a d (1982) Nature (London) 295, 66-68 21 Antel, J., Oger, J. J-F., Jaekevicius, S. a al. (1982) Pr0¢. NatlAcad. Sd. USA 79, 3330-3334 22 Fujinami, R. S. and Oldstone, M. B. A. Unpublished results 23 Nepom, J. T., Weiner, H. L., Diehter, M. A. stal. (1982),]. Exp. Med. 155, 155-167 24 Johnson, R. T., Griffin, D. E., Hirsch, R. L, aal. (1984) New Eng/and J. Med. 310, 137-141 25 Van Alstyne, D., Dyck, I. M., Berry, K. etal. (1983) Neuro/o~, 33, Suppl. 2, 195, Abstr. 26 Suckling, A. J., Pathak, S., Jagelman, S. etal. (1978)J. Neurol. Sdmwes 39, 147-154 27 Sobel, R. A., Blanchette, B. W., Bhan, A. K. etal. (1984),]. Immunol.

132, 2392-2401; 2042-2407 28 Fierz, W., Fontana, A. and Wekerle, H. (1984) Neurolog~34, 257. Abstr. 29 Neta, R., Salvin, S. B. and Sabaaw, M. (1981) Cell. Immunol. 64, 203-219 30 Bevan, M. J. (1984) Immunol. Today 5, 128-130 31 Husby, G., van de Rijn, I., Zabriskie, J. L. etal. (1976)J. Exp. Med. 144, 1094-1110 32 Stefansson, K., Dieperink, M. E., Richman, D. P. and Marton, L. S. (1984) Abstr. Soc. Neurosa, 14th Annual Meeting, Anaheim, p. 291. 33 Cerruti-Sola, S., Kristensen, F., Vandevelde, M. a al. (1983)J. Neuroimmunol. 4, 77-90 34 Watanabe, R,, Wege, H. and ter Meulen, V. (1983)Nature(London)305, t50-153 35 Waksman, B. H. (1983)Annals Neurol. 13, 587-591 36 Haspel, M. V., Onadera, T., Prabhakar, B. S. etal. (1983)Science 220, 304-306 37 Ben-Nun, A., Wekerle, H. and Cohen, I. R. (1981) Eur.J. lmmunol. 11, 195-199 38 Mokhtarian, F., MeFarlln, D. E. and Rains, C. S. (1984) Nature (London) 309, 354-358 39 Richert, J. R., McFarland, H. F., McFarlin, D. E. etal. (1983) Prof. Nail Aead. S,:i. USA 80, 555-559 40 Fuehs, S., Sehmidt-Hopfeld, I., Tridents, G. etal. (1980) Nature(London) 287, 162-164 41 Richman, D. P. and Amason, B. G. W. (1979) Pro~. NatlAcad. Sd. USA 76, 4632-4635 42 Goetzl, E.J., Blalock, J. E. and Feldman, J. eds. (t985)Conference on Neuromodulation of Immunity and Hypersensitivity J. Immunol. (in press) 43 Stefansson, K. and Arnason, B. G. W. (1984) in ComprehensiveT~'tbookof Onco/ogy(Moosa, A. R., Robson, M. C. and Schirupff, S. G., (eds), Williams and Wilkins, Baltimore (in press) 44 Kornguth, S. E., Klein, R., Appen, R. aal. (1982) Career50, 1289-1293 45 Johnson, R. T. (1983) in Vimm and Dtm~linating Disuses (C. A. Mires, M. L. Cuzner and R. E. Kelly, eds), pp. 7-19, Academic Press, New York

High connectivity within the network? In the ten year period following the twin revelations of M H C restriction and the idiotypic network, which led to the demise of horror autotoxicus, many of the far-reaching implications of M H C restriction have been fully validated andJerne's enlightening and encompassing view into the 'web of V domains' has proven amazingly prescient. Despite this, at both the T- and B-cell levels, we are still at the dawn of understanding the influences that are paramount in establishing the constitution of the mature immune repertoire. It is commonly granted that T-cell recognition is self-referential and chimera experiments have shown that each individual learns which M H C and Igh entities it will regard as self. In addition, the M H C molecules serve as part of an overall sign (semiotic") system whose rules govern intracellular communication, directing T-cell interactions into appropriate and unambiguous channels. We may also arbitrarily divide idiotypic affairs into their self-referential and semiotic aspects. Some students of the network consider that it is an autonomous whole, coordinating the activities of its members and embodying the whole organism. It is one of the engaging dualities of the immune system that its overall plan exploits the recognition of its own receptors, while these receptors concurrently play a decisive role in addressing the external world. It has been difficult to establish the balance between the autonomous aspects of the network and ks semiotic function of providing signs for intercellular recognition, especially between T-cell ~Semiotics is the study of signs and codes ~. Following Tada 3, 'immunosemiotics' can be defined as the study of the signs used in communication between immunologically active cells. © 1984,ElsevierSciencePublishersB.V.,Amsterdam 0167- 4919/84/$02.00

subpopulations, or between T and B cells. One recent idea in accord with this aim has been that certain 'regulatory idiotopes' 4 are different from others in serving as recognition sites for T cells, uniting T regulatory circuitry with the B receptor idiotypic universe. Predominant idiotypes, in part, result from such an organization, ensuring regulatory simplicity: instead of an idiotypic Tower of Babel, cells can speak to each other in a few key languages. In a fascinating recent report, Antonio Coutinho and his colleagues 5 have addressed an important issue which may relate to both the autonomous and coordinative aspects of the network: does the system start out as a network in ontogeny, in the absence of external antigenic stimuli? An essential property of such a formal network would be connectance among its members. As the repertoire expands, although each new receptor specificity might fit somewhere within the web of V domains, connectance - defined as the chance that any two idiotopes would interact with each other - must decrease. Therefore, Holmberg e t a l . 5 focused on the normal neonatal repertoire, expecting to detect the highest connectance at that time, their underlying assumption being that this would result from the stimulatory interplay of idiotype and anti-idiotype within the network. They have studied the reactivity between IgM molecules, presumably owing to their complementary V regions: a group of 70 from a collection of 112 monoclonal (Mab) IgM preparations from four 6-day old littermates were distributed in the solid phase a n d reacted with 9 Mab from the collection, each of which had been conjugated to

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anti-peroxidase to permit subsequent ELISA assay of inter-IgM rectivity. The results were striking and indicative of a very high degree of connectance. 5 of the 9 IgM conjugate preparations (the 'promiscuous set') reacted with a very high proportion of the panel of 70, 45% on the average. The most reactive IgM antiperoxidase conjugate bound to 2 out of every 3 IgMs. Reactivity of the non-promiscuous set was at a tenfold lower frequency. Looked at in another way, many of the panel of 70 reacted with none or only one of the conjugates. Within the group of IgM molecules isolated from a single mouse, both promiscuous and nonpromiscuous Mabs could be found. In general, the reactivity was of low affinity but a few interactions approached the range of typical antibodies. One pair of IgM molecules from the same mouse was examined in extenso and their reactivity could be attributed to V region interactions. These results suggest an exceptional degree of connectivity in the neonatal repertoire for at least one subgroup of IgM molecules and a high degree among most of the others. Because of the low level of interaction between the large majority of positives (despite being at least three times the background), it is not easy to assess the significance of the binding and whether it truly reflects interactions which could lead to intercellular stimulation or establishment and propagation of the network. Although cognizant of these limitations, the authors conclude that this level of interaction among normal antibodies in the neonate was predictable from network theory. It can be argued that it is difficult to contrive solid support for any specific level of connectivity, although a frequency of 1/20 (the non-promiscuous interaction ratio) somehow strikes a more reasonable chord than reactivity with every other antibody (the promiscuous set). Attempts to achieve a firm estimate of connectivity are subject to influences whose quantitative impact is still unknown. The spleen of the mouse during its first 6 days is probably undergoing more cataclysmic change than at any other time in life. The number of B cells quadruples from day 3 to day 6 as the heritable and regulated expression of a multiplicity of B-cell receptors continues apace. Clonotypes emerge according to a schedule which may be a consequence of gene order on the chromosome, and which is reproducible among syngeneic mice 6. Therefore, at the moment of hybridization (6 days) in the experiments of Holmberg et al., a considerable repertoire diversity already exists which could lead to a low connectivity between any two individual clones. The intrinsic, developing cohort is also subject to a powerful 'external' influence from maternally acquired idiotypes and anti-idiotypes. This influence may be positive or negative, as Rajewsky and his group 7 have shown that nanogram levels of idiotypic antibody molecules stimulate B cells whereas microgram and higher quantities are inhibitory. Crude assessment of the comparable sensitivity of T cells suggests that their activation threshold may be several orders of magnitude lower. Bona's group 8 has demonstrated the activation of idiotype-recognizing helper T cells by neonatal administration of idiotype: whether such activation, via maternal Ig, affects the early emergence of the repertoire remains to be established. Meanwhile, the entire

neonatal system during the first week of life is under the influence of high suppressor cell activity and poor antigen-presenting cell functiong: tolerance is being established as well as anti-idiotypic down regulation1°. In sum, the multiplicity of contrasting effects conspires to complicate calculations of repertoire frequency and connectivity. Nevertheless, the data 5 of Holmberg et aL, demand a focus on cases where high frequency recognition may plausibly explain a set of receptor interactions showing very high connectivity: two different ones come to mind. Recent experiments of Perlmutter et al. 11 show that a single V H gene family, M21, accounts for more than 70% of the initial V H gene rearrangements in late fetal life. Although gene diversification rapidly ensues so that by day 2 after birth, the proportion of M21 falls to 20%, it may be that a 'family-specific' V region marker activates rounds of complementary idiotypic induction, leading to the 'promiscuous' result; such a possibility bears exploration. A second possible source of high connectivity may derive from recognition receptors that serve the guidance function 12 within the semiotic system for intercellular recognition. In addition to M H C and Igrelated determinants, it has been suggested that differentiation antigens and their receptors ~ or vital growth receptors ~4may be recognized at high frequency within the system: if so, such events could play a major role in initiating network expansion. (The simplifying assumption is made that T-cell and B-cell idiotypic interactions are equivalent). It can be hoped that the intriguing results of Holmberg et aL will be expanded with comparisons to adult connectivity, study of maternal influences, and results from other laboratories examining T-cell and B-cell repertoire acquisition. Far-reaching insights into the autonomous and semiotic patterns of flae inner life of the immune system should follow. [] ELI SERCARZ

Department of Microbiology,

University of California, Los Angeles, CA 90024, USA

References 1 Jeme, N. K. (1976) Haroey Lectures Series 70, Academic Press, New York, p. 93 2 Eco, E. U. (1979)A Th~ty of SemioticsIndiana Univ. Press, Bloomington 3 Tada, T. (1982) in Immunogenaics (Bcnacerraf, B., Masson, eds) 4 Bona, C., Heber-Katz. E., and Paul, W. E. (1981)J. Exp. Med. 153, 951 5 Holmberg, D., Forsgren, S., Ivars, F. and Coutinho, A. (1984)J. Immunol. 14, 435 6 Canero, M. P., Wylie, D. E., Gerhard, W. and Klinman, N. R. (1974) Proc. Natl Acad. Sd. USA, 76, 6577 7 Rajewsky, K. and Takemori, T. (1983)Ann. Rev. Immunol. 1,509 8 Rubinstein, L. J., Yeh, M. and Bona, C. A. (1982).]. Exp. Med. 156, 5O6 9 Argyris, B., Immunol Today (1984), 5, 34 10 Pullok, B. A., Stohmr, R. and Kearney, J. F. in (1984)Idiotypy in BioloD, and Medicine (Kohler, H., Urbain, J. and Cazenave, P.-A., eds) Academic Press, New York p. 187 11 Perlmutter, R. M., Kearney, J. F., Chang, S. P. and Hood, L. E., unpublished 12 Mitchisun, N. A. (1980) in Strategiesof Immune Regulation (Sercarz, E. and Canningham A. J., eds) Academic Press, New York 13 Serearz, E. (1984) in Regulation of the Immune System (Cantor, H., Chess, L. and Sercarz, E., eds) Alan Liss, New York (in press) 14 Coutinho, A., Fomi, L., I~l~berg, D., Ivars, F. and Vaz, N. (1984) Immunol. Revs 79, 151