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ALTHOUGH the chicken is more closely related to dinosaurs and crocodiles than to the mouse1, the clear-cut demarcation between thymus-derived (T) and bursa-derived (B) lymphocytes in this bird2,3 offers an excellent system for study of the two lymphocyte types. B cells have been demonstrated to possess surface immunoglobulin3–5, while T cells have not, although it has been established that light chains at least are expressed on specifically activated chicken T cells6. So far, however, intact polypeptide chains have not been demonstrated on T and B cells. We now describe the isolation and partial characterisation of surface immunoglobulins of chicken B and T lymphocytes. We have evidence that both lymphocyte types have surface immunoglobulins consisting of light chains, μ chains and a heavy chain of molecular weight 40,000.

THE question of how the female stigma of the plant recognises a pollen grain carrying a compatible male gamete from all the possibilities presented to it by air currents and visiting insects is an intriguing problem1. When pollen is recognised at the stigma surface, a mixture of components, including proteins and glycoproteins, are released from cavities in the pollen walls2,3. These components have been partially characterised4,5 and include those essential to the recognition process6. The pollen wall components flow over and bind to the stigma surface which is covered by a secreted sticky coating7. The binding of specific recognition factors determines the success of a mating8. We have attempted to identify factors involved in poller-stigma recognition, using immunochemical methods with rabbit antisera to pollen and stigma surface components. The major antigen of the stigma surface shows immunological identity and has the same molecular weight as an antigenic pollen wall component. This stigma antigen is also partially identical with components of other tissues of the same plant. Absorption experiments show that the cross-reacting antibodies can be removed from the antisera, leaving antibodies which interact only with the immunising antigen. This raises the question whether plant cells, like animal cells9, are specified according to their family, species, organ and tissue by surface determinants.

RECENT studies1–4 have shown that antibody production and tolerance to polypeptide antigens can be induced simultaneously. Furthermore, the dosage of antigen seems to determine which of these phenomena predominates. Tolerance can be induced by either small or large dosages of antigen. Challenge with an intermediate concentration of antigen results in the production of antibody. Various hypotheses, including different cellular mechanisms for the induction of immunity and tolerance3,5 and a means of concentrating antigen3, have been proposed to explain these findings. We discuss here a theoretical interpretation of these events which attributes the degree of tolerance or antibody formation to the statistical distribution of antigen molecules among the potentially reactive cells.

GENES controlling specific immune responsiveness at the level of activation of the thymus derived (T) lymphocyte, and collaboration of these cells with lymphocytes derived from the bursal equivalent (B lymphocytes), have been shown to be linked to the major histocompatibility complex (MHC) in many species1. The mechanism of action of these genes is not understood, and it has been postulated that they represent structural genes for a non-immunoglobulin receptor for antigen on T lymphocytes2.

IN spite of all the immunological studies which have been carried out with poikilothermic vertebrates, there have been no quantitative studies of the induction of tolerance to purified anitgens, yet such studies might account for the difficulties often encountered in the immunization of lower vertebrates. Moreover, they should have a direct bearing on the phylogenetic emergence of the mechanisms involved in this crucial aspect of immunity. In this article, we shall show that adult marine toads (Bufo marinus) can be made tolerant to bovine serum albumin (BSA) by pretreatment with supraoptimal doses of the antigen.