Evidence for a regulatory role of the T8 (CD8) antigen in antigen‐specific and anti‐T3‐(CD3)‐induced lytic activity of allospecific cytotoxic T lymphocyte clones

Abstract

The functional role of the T8 antigen of human T cells was studied by inhibition with anti-T8 monoclonal antibodies (mAb) of the cytotoxic action of T8+ cytotoxic T lymphocyte clones (CTL). All clones were allospecific and directed against HLA-B7. The ability of seven different anti-T8 mAb to inhibit the cytotoxicity of these alloreactive CTL clones corresponded with their avidity for a particular target cell. The lysis of cross-reactive antigen-bearing target cells was more readily blocked by anti-T8 mAb than lysis of the specific B7 target cell against which a clone was raised. The seven anti-T8 mAb showed a spectrum of CTL blocking ability ranging from strong blocking with all five CTL clones tested to weak inhibition of only two out of five clones. mAb inhibition of CTL reactivity and cold target inhibition studies with one of the five CTL clones indicate a post-binding role of the T8 molecule. Functional epitope mapping based on CTL blocking with the anti-T8 mAb resulted in the definition of one nonfunctional epitope on the T8 molecule which is only expressed on mature T lymphocytes and a cluster of closely related functional epitopes expressed on both thymocytes and mature T lymphocytes. Not only allospecific cytotoxicity, but also nonspecific cytotoxicity induced anti-T3 mAb in these allospecific clones was inhibited by anti-T8 mAb in the absence of HLA class I expression on the target cell (Daudi cell line). The hierarchy of blocking with anti-T8 mAb and the classification of functional epitopes on T8 in anti-T3-induced nonspecific cytotoxicity were similar to those obtained in blocking of allospecific reactivity of the CTL clones. This analogy points to an identical function of the T8 antigen in both allospecific and anti-T3-induced nonspecific cytotoxicity. If HLA class I molecules are the counter structures of the T8 antigen, then these results argue against an adhesion-like function of the T8 structure. The combined results show that the T8 molecule has a regulatory role in CTL activation. It is postulated that the T8 antigen might serve as a receptor that transduces a negative feedback signal for T cell activation which prevents T cell triggering by nonspecific interaction.

Anti-CD8 Antibodies Can Trigger CD8+ T Cell Effector Function in the Absence of TCR Engagement and Improve Peptide–MHCI Tetramer Staining

“…Previous studies have shown that anti-CD8 Abs retain their effects in the absence of a pMHCI/CD8 interaction (26,(53)(54)(55). In this study, we confirm that the enhancing effects of OKT8 on HLA A*0201 tetramer on-rate at the cell surface are still apparent in the context of CD8-null MHCI molecules (Fig.…”

Clonal heterogeneity of HLA-B27 cellular allo-recognition. Delineation of immunodominant sites

“…However, the lysis of LH cell is totally inhibited by anti-CD3 and anti-CD8 mAb, whereas lysis of the B27.1 target LG15 was only partially inhibited by anti-CD8 mAb (Table 3). This phenomenon was also observed recently with another CTL clone [29]. This result may be interpreted in two ways: (a) blocking by anti-CD8 mAb reflects differences in avidity in a more sensitive way than cold target inhibition experiments, and (b) inhibition of lysis by anti-CD8 mAb would not only reflect avidity of effector-target interaction but would have additional effects on post-binding steps, as has been previously suggested [29,301.…”

Rapid cloning of HLA-A,B cDNA by using the polymerase chain reaction: frequency and nature of errors produced in amplification.

“…This suggests that many ofthe differences between the PCR and the cDNA sequences are artefacts of the cDNA analysis (21). Our analysis of 10 PCR HLA-B7 cDNA sequences does not support the suggestion that JY expresses two distinguishable HLA-B7 alleles (22).…”