Enrichment of hapten-specific helper T cells using anti-immunoglobulin combining site antibodies

Generalization of single immunological experiences by idiotypically mediated clonal connections

Clonal interactions of B cells by idiotope-specific mutual recognition of their antigen receptors with the participation of T cells were assumed to form a web of unknown density, referred to as the idiotypic network. Although these clonal connections were proposed to fulfill important internal regulatory functions, their biological significance, especially in relation to antigen-induced immune responses, remained a mystery. In view of this, we postulate that the basic function of the idiotypic internal connection between B and T cell antigen receptors is to transform antigen-induced cellular activations, by idiotypic crossreactivity, into the regulation of cell clones with different antigen specificities. This process leads not only to the suppression of major clones but also to the activation of minor ones. The latter activating property may allow the generalization of single antigenic experiences, so that the immune system in its entirety benefits in its battle against environmental microbes. Such idiotypic clonal interactions are particularly effective in early ontogeny. During a short neonatal imprinting period, maternal immunological knowledge in the form of somatically mutated, high-affinity IgG antibodies, acquired through a continuous encounter with external antigens, guides the initial ontogenetic development of the immune system and so exerts long-lasting transgenerational advantageous effects in the offspring.

Autoreactive or self restricted?

Putative major histocompatibility complex (MHC) class II-specific T cell clones were isolated from nominal antigen-primed T cell populations propagated in vitro under antigen selection. However, unlike the proliferative responses of nominal antigen-specific, MHC class II-restricted T cell clones derived from the same population, the former's MHC-specific proliferative responses required that the culture medium be supplemented with serum. The role of xenogeneic antigens in the generation of this category of "autoreactive" T cells is discussed.

Thymus-independent induction and antigen-dependent recovery of idiotype-specific suppression

BALB/c nude (nu/nu) mice and euthymic (nu/+) littermates were treated as neonates with anti-T15 antibody and challenged at various ages with either a thymus-independent, PC-Brucella abortus (PC-BA), or thymus-dependent, PC-keyhole limpet hemocyanin (PC-KLH), form of phosphorylcholine (PC). Nu/nu mice challenged with PC-KLH received KLH-primed splenic T cells prior to immunization. Neither neonatally anti-idiotype-treated nu/+ nor nu/nu mice responded with the production of T15-positive anti-PC antibodies after challenge with either form of PC antigen. It is concluded that neither induction nor maintenance of a state of T15-specific suppression requires thymus-matured T cells. Recovery of anti-PC responsiveness in suppressed nu/+ or nu/nu mice was similar and was found to be related to the form of antigen used to elicit the response. Immunization with PC-KLH revealed a long-lasting unresponsiveness (up to 16 weeks). In contrast, immunization with PC-BA elicited a full anti-PC response as early as at 6.5 weeks of age.

Idiotypic relationship of anti-Ia.2 antibodies

Alloantiserum and hybridoma-derived anti-Ia antibodies were investigated for their idiotypic similarity using 4 monoclonal anti-idiotypes raised against monoclonal anti-Ia. With one anti-idiotype, idiotypic cross-reactivity could be found between three independently derived monoclonal BALB/c anti-Ia antibodies, all of which were directed against the same serological determinant, Ia.2. The respective idiotype, tentatively designated Ia.2 idiotope, could also be demonstrated on anti-Ia.2 antibodies in BALB/C alloantisera, but not on anti-Ia against other specificities. The expression of the Ia.2 idiotope is linked to the Igh allotype; the use of Ig-recombinant mice allowed us to map the Igh-Ia.2 locus to the left of the T15 marker in the Igha V region.

Demonstration of T15 idiotype-positive effector and suppressor T cells for phosphorylcholine-specific delayed-type hypersensitivity response in CBA/N or (CBA/N X BALB/c)F1 male mice

Subcutaneous immunization of CBA/N or (CBA/N X BALB/c)F1 (NBF1) male mice, which were defective in phosphorylcholine (PC)-specific humoral antibody response, with PC-conjugated syngeneic spleen cells induced a PC-specific delayed-type hypersensitivity (DTH) response, while intravenous administration of the same cells induced PC-specific suppressor T cells for the DTH response. Treatment of PC-specific effector or suppressor T cells for the DTH response induced in NBF1 male mice with anti-T15 idiotypic antibody inactivated effector or suppressor functions of these T cells implying that PC-specific T cells in NBF1 mice expressed T15 idiotypic determinants on their surface. Enrichment of PC-specific suppressor T cells was also shown by employing anti-T15 antibody-coated dishes.