T suppressor factor activity is due to two separate molecules. The Lyt-1(-)2+I-J+ cells of mice primed with antigen make an antigen binding molecule which is only active when complemented by cofactor made by Lyt-1+2(-)I-J+ cells

Functional equivalence of cryptococcal and haptene-specific T suppressor factor (TsF). I. Picryl and oxazolone-specific TsF, which inhibit transfer of contact sensitivity, also inhibit phagocytosis by a subset of macrophages

Monoclonal and conventional cryptococcal-specific T suppressor factors (TsF) (also called TsFmp) depress phagocytosis by a subset of macrophages, while picryl- and oxazolone-specific TsF depress the passive transfer of contact sensitivity. This paper shows that these haptene-specific TsF also inhibit phagocytosis by a subset of macrophages and, using this assay, that the anti-haptene TsF resemble the anti-cryptococcal TsF in five respects: (i) the need for reexposure to specific antigen to trigger the release of TsF; (ii) genetic restriction in action; (iii) possession of an antigen-binding site; (iv) expression of I-J determinants; and (v) inactivation by reduction and alkylation. Purification of the anti-picryl TsF by sequential affinity chromatography indicates that the inhibition of phagocytosis is due to the TsF itself and not to a TsF-antigen complex. The TsF inhibits phagocytosis by a direct action as macrophages treated with TsF and exposed to antigen do not release a second factor which inhibits phagocytosis. These results and those of the accompanying paper indicate that the anti-cryptococcal and anti-haptene TsF are functionally equivalent, antigen-specific suppressor factors.

Unique Ia epitopes of T cells (Iat) are involved in the recognition of stimulator cells in the allo-MLR

Anti-Iat monoclonal antibodies (mAbs) were found to block the recognition phase of allogeneic mixed lymphocyte reaction (allo-MLR) by reacting with responder T cells but not stimulators. The inhibitory pattern was dependent on the major histocompatibility complex (MHC) of both the responder and stimulator cells. Certain molecules, including IgVH and I-J of stimulator cells were also important. It is suggested that Iat epitopes on alloreactive T cells may serve as a marker of a novel type of a T cell recognition site for Ia. The model of T cell receptor complex with two distinct sites for MHC recognition is proposed.

A alpha and A beta class II I-A determinants of antigen-specific T-helper factor and its antigen-nonbinding chain

Antigen-specific T-helper factor (ThF) of CBA (H-2k) origin in the picryl (TNP) contact sensitivity system (Mr 60-70 kDa) was reduced with dithiothreitol under mild conditions. Affinity chromatography on antigen yielded an antigen-binding chain (Mr 20-30 kDa) and an antigen-nonbinding chain (Mr 40-50 kDa). Both chains were glycoproteins and were bound by lentil lectin. Affinity chromatography on anti-I-A monoclonal antibodies showed that I-A determinants occurred on the complete molecule and on the antigen-nonbinding, but not on the antigen-binding, chain. In contrast, five different monoclonal antibodies to I-E alpha failed to absorb ThF. Moreover, the complete molecule and the I-A+ antigen-nonbinding chains had determinants of the alpha and beta chains of I-A and conformational determinants which are based on both chains. Sequential absorption and elution showed that A alpha and A beta determinants occurred on the same molecular complex. These data suggest a minimal model of ThF as a two-chain disulfide-bonded structure with an antigen-binding chain and a separate I-A+ antigen-nonbinding chain which behaves as a single unit in phosphate-buffered saline and has elements of both A alpha and A beta.

Production of T suppressor factor specific for the hapten picryl chloride requires both T suppressor cells and an antigen-specific, genetically restricted second signal

We investigated the requirement for activation of T suppressor cells specific for the hapten picryl chloride and the release of hapten-specific T suppressor factor. Using an in vivo experimental system, we report that activation of T suppressor cells and the consequent release of T suppressor factor required two signals: one was provided by primed T suppressor cells, i.e. spleen cells from mice injected with the tolerogen picrylsulphonic acid, and the other was provided by the specific antigen in the context of H-2 gene products. Mechanisms by which the interaction between these two signals led to activation of T suppressor cells and the production of T suppressor factor, as well as a comparison with other antigen-specific suppressor systems, are discussed.

General considerations in the interpretation of I-J genetic restrictions: evidence that the antigen-binding chain of antigen-specific T-suppressor factor has two recognition sites for members of the I-J hierarchy

(CBA X B10)F1 [(H-2k X H-2b)] mice produce two types of antigen-specific T-suppressor factor (TsF), which can be separated by affinity chromatography on anti-I-J monoclonal antibody. After reduction and alkylation, both chains of F1 TsF are required for biological activity. However, the antigen-binding chain (AgBC) of F1 TgFk (AgBCk) is only complemented by I-Jk and likewise for F1 TsFb. In other words, interchain complementation shows the same genetic restriction in interchain complementation in parental and F1 mice. F1 TsF bearing, for example, I-Jk (TsFk), interacts with haptenized 'antigen-presenting cells' ('APC') and parental I-Jk chains interacts with haptenized 'APC' of both parental haplotypes (dual reactivity). In contrast, the combination of parental AgBCb and F1 I-Jb shows single reactivity and only interacts with haptenized 'APCb'. It was inferred that the antigen-binding chain is responsible for the dual reactivity and, hence, for the interaction with a member of the I-J hierarchy on the 'APC'. It was concluded that the antigen-binding chain of TsF has two recognition sites for members of the I-J hierarchy--one for interchain complementation and the other for interaction with the haptenized 'antigen-presenting cell'. The term member of the I-J hierarchy is used instead of I-J because it is not clear whether the AgBC interacts with I-J or a receptor for I-J, or indeed a receptor for that receptor.

A novel suppressive activity: complementation between a T cell induced with first-order T-suppressor factor and an I-J-restricted antigen-nonspecific T cell

Previous studies demonstrated that the first-order T-suppressor factor (TsF1) requires the presence of antigen to induce idiotype-specific Ts cells which readily suppress phenyltrimethylamino (TMA) hapten-specific delayed-type hypersensitivity (DTH) responses when transferred into already immune recipients. In this study we show that TsF1 in the absence of antigen induces a splenic population which limits DTH in recipient mice only when an additional accessory lymphoid population was also cotransferred. Neither of these populations alone was sufficient to mediate suppression and depletion of T cells in either population's abrogated suppression, indicating the T-cell dependency of the complementing cell types. Moreover, suppression was seen only when TMA-TsF1-induced and not normal spleen cell lysate-induced cells were cotransferred with the antigen-induced population, suggesting the requirement for a specific signal to induce the factor-induced population. Further experiments showed that the antigen-induced lymphoid population could be replaced by either heterologous antigen-induced or adjuvant alone-induced splenic populations, indicating the lack of specificity of this secondary population. Further analysis showed that the cell complementation between TMA-TsF1-induced and the nonspecific accessory lymphoid population resulted in antigen-specific and genetically restricted immune suppression. The TsF1-induced lymphoid population was not responsible for the genetic restriction, and furthermore, there was no restriction observed between the two complementing populations. However, matching of the nonspecific accessory cell with the recipient host at the I-J subregion of the H-2 complex was essential for immune suppression. Finally, the activity of complementing cells was found to be independent of cyclophosphamide-sensitive Ts populations of the recipient mice. The ramifications of these findings with reference to the existing suppressor pathways are discussed.