The receptor specificity of alloreactive T cells. Distinction between stimulator K, I, and Dr Products and degeneracy of third-party H-2 recognition by low-affinity T cells

Abstract

The specificity of binding of stimulator-derived H-2 antigens by mixed lymphocyte culture (MLC)-activated T blasts was investigated under conditions of antigen excess. We have shown that the detectable proportion of alloantigen-binding blasts from primary MLC is a function of antigen concentration, and can represent up to more than 90 percent of total blasts, when the antigen is presented in the appropriate form (on mitomycin-treated viable stimulator cells, or membrane vesicles prepared from lipopolysaccharide blasts), and at nonlimiting concentration. Thus stimulator alloantigen-binding directly parallels the proliferative response and is not restricted to a subpopulation of T blasts. However, the marked dependence of the binding on antigen concentration indicates that cells with a wide range of receptor affinities for the stimulating determinants are involved. In view of this possibility, the specificity of binding by these cells was studied. We have demonstrated that stimulator K, I, and D region products are bound by nonoverlapping subpopulations of blasts, the sum of which may represent 93 percent of total blasts. Thus, specific distinction by these cells between different H-2 region products is not affected by the putative heterogeneity in terms of receptor affinities. However, specificity with respect to unrelated H-2 haplotypes is strictly dependent on antigen concentration. A preferential binding of stimulator membrane vesicles occurs at limiting concentrations; whereas the majority of blasts bind stimulator and third- party vesicles equally well at high vesicle concentrations. The binding of both vesicle types is specific in that it can be inhibited with the relevant anti-H-2 sera. Furthermore, stimulator and third-party vesicles seem to compete for binding sites on the same cells, as shown by cold antigen inhibition. From these results, we propose that there is an imperfect distinction between stimulator and third-party H-2 antigens by the majority of primary MLC blasts. In contrast, highly selected long-term MLC blasts do not bind third-party H-2 antigens at any concentration, and seem to have high affinity for the stimulating antigens. We conclude that large numbers of clones with low-affinity (cross- reactive) receptors are generated in primary MLC, most of which become eliminated during long-term selection. This implies that the frequency of cells strictly specific for nonshared stimulating determinants must be minute.

Regulatory mechanisms in cell-mediated immune responses. Role of I-J and I-C determinants in the activation of H-2I and H-2K/D alloantigen-specific suppressor T cells.

“…Such an interpretation also requires that initial priming involve presentation of shed allogeneic class I molecules on I-C + Ts host cells, since the original priming cells are fully H-2 allogeneic. Shedding of MHC determinants (26) and reorientation and recognition of these shed alloantigens on host cells have been documented by others (27)(28)(29).…”

T cell idiotypes recognizing self‐major histocompatibility complex molecules: H‐2 specificity, allotype linkage, and expression on functional T cell populations

“…Nagy, unpublished results). Thus the antiserum appears to recognize low affinity receptors for H-2k that are expressed by a large proportion of primary MLR blasts [17]. In this report it is demonstrated that the very same 5936' anti-H-2k receptors are expressed on H-2k T cells recognizing antigen in an MHC-restricted fashion.…”

“…To remove passively bound stimulator antigens [17,201 and self-Ia antigens [8,91, the cells were treated with trypsin, and incubated overnight in fresh medium containing IL2 (see Sect. 2.6).…”

“…SC stimulation with concanavalin A (Con A) and lipopolysaccharide (LPS) was performed as previously described [17].…”

Lyt phenotypes of primary cytotoxic T cells generated across the A and E region of the H‐2 complex

“…Without washing, 1 volume of selected nontoxic rabbit serum (diluted 3 : 11 in medium) was added and the incubation continued for 60 min at 37°C. The cells were then washed, counted, and their viability was detrmined by fluorescein diacetate staining [14].…”