Constitutive functional heterogeneity without detectable somatic mutation of antigen receptor genes in helper T cell clones: possible regulation by novel HLA class II "DY" determinants

Human T-cell clones in long-term culture as a model of immunosenescence

We have consistently observed that like other normal somatic tissue cells, human T lymphocytes manifest a finite proliferative capacity in culture in vitro. When measured in population doublings (PD), this averages about 35 PD for T-cell clones (TCC) derived from mature peripheral T cells of young adults and about 20 PD more for TCC derived from T-cell precursors in their bone marrow. We believe that alterations in surface marker phenotypes and corresponding functional changes observed in these human TCC as they progress through their finite lifespans in vitro can provide valuable information on processes of T-cell immunosenescence in vivo. They may also provide a model system for studying ways of modulating the ageing process to delay or prevent immunosenescence in the elderly and the chronically infected or possibly to accelerate immunosenescence in organ transplantation.

Analysis of the HLA-DR gene locus by temperature gradient gel electrophoresis and its application for the rapid selection of unrelated bone marrow donors

The human leucocyte antigen (HLA) class II compatibility of bone marrow donor and recipient is an essential prerequisite for the prevention of severe graft versus host disease and therefore for the successful outcome of bone marrow transplantation. In this study an efficient protocol was developed for the rapid analysis of the polymorphic HLA-DR gene locus, based on DNA-polymerase chain reaction (PCR) amplification of the variable exon II of the HLA class II DR genes and subsequent temperature gradient gel electrophoresis (TGGE). Computer-assisted melting map calculations were carried out to determine the melting behavior of the different HLA-DR fragments. Despite the high variability of the DR alleles on the nucleotide sequence level the calculations revealed a common melting domain structure of the different HLA-DR fragments, which was experimentally confirmed by perpendicular TGGE. On parallel TGGE, all samples were separated under the same electrophoretical conditions using a single PCR fragment without GC-clamp. TGGE was applied for the analysis of the DR alleles of numerous bone marrow receipt pairs and compared to the corresponding serological and DNA typing results. The TGGE patterns were found to be different for all samples with different HLA-DR typing results. Identical homoduplex and heteroduplex patterns occurred only in the case of complete genotypic HLA-DR identity as determined by direct sequencing of PCR products.

Involvement of "accessory" and antigen receptor molecules in human helper T cell clone activation studied by monoclonal antibody inhibition

The requirements for activation of autocrine proliferation in human helper T cell clones (Th-TCC) by allogeneic cells were examined in monoclonal antibody (MoAb) blocking studies. Stimulation was not blocked by CD4, CD5, CD6, CD7, or CD45 MoAbs, despite high levels of expression of these antigens on the TCC. Only CD2 and CD11a (LFA-1) MoAbs blocked activation, the latter only when peripheral blood mononuclear cells (PBMCs) and not B-lymphoblastoid cell line (B-LCL) cells were used at stimulators. Responses to interleukin 2 (IL 2) were only minimally blocked by any of the MoAbs. All TCC were CD3+ and expressed the alpha/beta chain T cell receptor (TCR) as detected by moAb WT31. Accordingly, CD3 and WT31 MoAbs consistently blocked stimulation by B-LCL, and in addition one anti-DR5 TCC and one anti-DQw3 TCC were blocked by MoAb 42/1C1, which is directed to an idiotypic determinant of the HPB-ALL leukemic line TCR. Only these two TCC reacted with moAb 42/1C1 in flow cytometry. These observations suggest that CD2- but not LFA-1-mediated interactions, as well as TCR and stimulating antigen binding, are absolutely necessary to activate Th-TCC.

DY determinants, possibly associated with novel class II molecules, stimulate autoreactive CD4+ T cells with suppressive activity

A set of T cell clones (TCC) isolated from HLA-DR-, Dw-, DQ-matched allogeneic MLCs was found to proliferate autonomously when stimulated with cells carrying a wide range of class I or II specificities. This apparently unrestricted proliferation was relatively weak, and only low levels of IL-2 were present in the supernatants of stimulated cells. Autologous as well as allogeneic PBMC and B lymphoblastoid cell lines (B-LCL) were capable of stimulating such clones, which were also restimulated by suppressive, but not by helper, TCC. Moreover, such clones displayed the unusual property of autostimulation. mAb inhibition experiments suggested that class II- or class II-restricted antigens were involved in stimulation. Thus, certain "broad" mAbs (TU39, SG520) reacting with multiple locus products inhibited activation of these reagents, but none of those reacting more specifically with DR (TU34, TU37, L243, Q2/70, SG157), DQ (TU22, SPV-L3, Leu 10), or DP (B7/21), or mixtures of these mAbs, were able to do so. Evidence from sequential immunoprecipitation experiments suggested that mAb TU39 bound class II-like molecules other than DR, DQ, and DP on TCC and B-LCL, and it is therefore proposed that such putative novel class II-like molecules may carry the stimulating determinants for these autoreactive clones. DY-reactive clones lacked helper activity for B cells but mediated potent suppressive activity on T cell proliferative responses that was not restricted by the HLA type of the responding cells. Suppressive activity was induced in normal PBMC by such clones, as well as by independent suppressive clones, which was also inhibited only by mAb TU39. These findings lead to the proposal that DY-reactive autostimulatory cells may constitute a self-maintaining suppressive circuit, the level of activity of which would be regulated primarily by the availability of IL-2 in the microenvironment.