Functional subdivision of HLA-DRw8 with influenza-specific cloned cell lines

Requirements for lysis of activated T cells by class-II-restricted cytolytic T-lymphocytes

In the present study, we explored the specific requirements for lysis of human activated T cells by CD4+ CTLs. This was achieved by using human CD4+ T cell lines or clones specific for a peptidic fragment of influenza virus as both CTL effectors and target T cells (TTCs). Our results further establish that human activated T cells expressing HLA-DR molecules can present Ag to and be lysed by CD4+ HLA-DR restricted CTLs. This killing is Ag specific and HLA-DR restricted. It can be observed whether TTCs are heterologous or autologous, CD4+ or CD8+. However, we find that in our model: (a) TTCs are able to present artificially processed peptidic fragments of Ag, but not the corresponding natural Ag in the context of class II determinants, even if they can process whole virus in the context of class I determinants; (b) TTCs must express high density of HLA-DR molecules on their membrane; (c) preincubation of TTCs with high concentrations of peptide is required; and (d) interestingly enough, addition of free peptide at similar concentration during the cytolytic assay to replace TTC preincubation inhibits TTC lysis by at least two different mechanisms, i.e., cold-target inhibition in which CTLs serve as their own cold targets and inhibition at the effector cell level. From these results, one can conclude that stringent conditions are required for lysis of activated T cells by class-II-restricted CTLs.

A cellular and functional split in the DRw8 haplotype is due to a single amino acid replacement (DR beta ser 57- asp 57)

The single DR beta chain gene of the DRw8 haplotype has been suggested to carry both the DRw8 and the DRw52 epitopes. Cellular typing has shown that the DRw8 haplotype can be split into three subtypes, Dw8.1, Dw8.2, and Dw8.3, presumably due to a polymorphism in the DRw8 beta chain. Furthermore, Dw8.1 and Dw8.2 cells present influenza virus antigen to different T-cell clones. In the present study, DRw8/Dw8.2 beta chain cDNA was cloned and characterized. A comparison of this sequence with a partial DRw8/Dw8.1 beta chain gene suggested that the DRw8 split is due to a single amino acid replacement of ser57-asp57 caused by three nucleotide substitutions in the same codon. In most DR haplotypes, two expressed DR beta chain genes exist. Comparing the nucleotide sequence of the single beta gene in the DRw8 haplotype to those of other DR beta genes revealed that the DRw8 beta gene sequence is most closely related to the DRB1 genes of the DR3, 5, and w6 haplotypes. However, the comparisons also showed that it was not possible from sequence similarities to divide the DR beta genes into two or more distinct allelic series.

Activation signals via CD2 molecule and interleukin 2 receptor act in synergy for helper function induction

The membrane CD2 molecule appears to play an important role in T cell activation. Indeed, T cell stimulation by some combinations of anti-CD2 monoclonal antibodies (mAb) can result in antigen-independent expression of helper function as assessed by proliferation and lymphokine secretion. We report here that T cell stimulation by a combination of two anti-CD2 mAb recognizing GT2 and T11(1) epitopes, respectively, cannot alone induce T helper clones to proliferate when preincubated in culture medium devoid of exogenous interleukin 2 (IL2). The concerted action of both anti-GT2 + T11(1) mAb and exogenous recombinant IL2 is required to induce cloned helper T cells to produce IL 2 and interferon-gamma to significantly increase IL2 receptors (IL2R) and finally to divide by an autocrine mechanism, whereas each signal alone has no effect. This therefore suggests that, under some conditions of CD2 stimulation, two minimal signals may be delivered through CD2 and IL2R and act synergistically to achieve a complete expression of T helper cell functions. Moreover, analysis of phosphatidylinositol and phosphatidic acid metabolic changes mediated by each signal separately or together suggests that, in this model, IL2 increases the phosphoinositide turnover induced by anti-CD2 antibodies up to a level required for helper function acquisition.

Both HLA-DR and HLA-DQ determinants contribute to HLA-Dw typing

The respective contribution of HLA-DR and HLA-DQ gene products in the induction of allogeneic proliferative responses in primary mixed lymphocyte reaction and, therefore, in HLA-Dw typing, is still unclear or controversial. This is in part due to a strong linkage disequilibrium between HLA-DR and -DQ genes. We used DR- or DQ-restricted influenza-specific T-cell clones to define DR and DQ products on a large panel of allogeneic antigen presenting cells. With this functional screening assay, we identified two haplotypes with unusual DR/DQ associations. Cells of these haplotypes were then used as responder cells in mixed lymphocyte culture and stimulated by homozygous typing cells displaying DR or DQ incompatibilities. Our results indicate that DR or DQ incompatibilities alone can give rise, in both cases, to strong T-cell proliferation in a mixed lymphocyte reaction. This was further verified by blocking experiments of secondary mixed lymphocyte reactions by HLA-specific monoclonal antibodies. Anti-DQ, but not anti-DR, antibodies inhibited DQ-incompatible responses. Conversely, anti-DR, but not anti-DQ, antibodies could block DR-incompatible mixed lymphocyte reactions. Together, the results suggest that both HLA-DR and DQ gene products can be involved in HLA-Dw typing. Finally, in dual DR- and DQ-incompatible mixed lymphocyte reaction combinations, HLA-DR molecules seem to have an immunodominant effect, because the response is mostly inhibited by anti-DR antibodies. Immunodominance of HLA-DR allodeterminants may, at least in part, explain some of the controversial conclusions reported by others concerning the role of HLA-DQ molecules in HLA-Dw typing.

Regulation of helper T cell clone proliferation via the CD2 molecule

We have investigated the requirements for CD2-induced proliferation of a CD4+, CD8-, CD3+, CD2+ antigen-specific, class II-restricted proliferating cloned cell line. A combination pair of two monoclonal antibodies (MoAb) recognizing, respectively, TII1 and D66 epitopes on the CD2 molecule was used as a stimulus. The regulatory function of accessory cells and various interleukins in this proliferation was determined. The results show that although this clone was able to proliferate in the absence of accessory cells (AC) or interleukin 1 (IL-1) when stimulated by these MoAb, AC constantly enhanced the response to these MoAb. AC acted by increasing high-affinity IL-2 receptor expression. On the contrary they did not play any role in IL-2 production. This regulation of IL-2 receptor expression by AC was specific of adherent cells, did not involve Fc receptors, was impaired when AC were metabolically inactivated and did not require T cell-AC interaction via LFA1, CD4, or HLA molecules. The AC function was not abrogated by anti-IL-1 antibodies and could not be replaced by exogenous IL-1. These results were compared to previously described AC effects on resting T-cell proliferation when stimulated with the same pair of anti-CD2 MoAb. Clear differences in activation requirements in resting and activated T cells via CD2 molecules were found.

An antiviral T-cell clone defines a functional supertypic specificity shared by different HLA-DR molecules from DR2-short, DRw11, and DRw13 haplotypes

An influenza virus-specific HLA class II-restricted human T4+ clone (Ij) allows us to define a new functional supertypic HLA class II specificity shared by three different haplotypes. Influenza A virus-infected antigen-presenting cells of these three haplotypes, HLA-DR2 short, DRw11, and DRw13, are able to stimulate Ij cells. The same precise viral specificity is seen in all three cases. Proliferation inhibition experiments using HLA-specific monoclonal antibodies demonstrate that HLA-DR products are involved in all cases. However, according to the DR specificity of the antigen-presenting cell, differential blockings by a series of DR-specific monoclonal antibodies suggest that the functional epitope is shared by different HLA-DR molecules. This is confirmed by two-dimensional gel analysis of the HLA-DR beta chains expressed in the three haplotypes.

Functional definition of HLA-DR and -DQ epitopes specific for DR2-short, DwFJO haplotype

T-lymphocyte clones specific for the influenza A/Texas virus were obtained by limiting dilution of activated T cells from an HLA A2/3,B7/39,Cw -/-,DR2-short/2 short,DQw1,DwFJO/FJO donor. Among the proliferating clones studied, and irrespective of their antigenic specificities, most of them were restricted by epitope(s) on HLA-DR molecules present only on DR2-short/DwFJO cells but not on DR2-negative or DR2-long positive (Dw2,Dw12,Dw-) cells. Two clones were restricted by epitopes borne by DQ products. Here again, these epitopes were present on DR2-short/DwFJO but not on DR2-long,DQw1 (Dw2,Dw12) cells, indicating that the DQw1 molecules of DR2-long and DR2-short haplotypes are different. Taken together, these results indicate that the DR2-short,DwFJO haplotype is characterized by both HLA-DR- and DQ-specific molecules. Finally, one clone was restricted by an epitope shared by DR products from DR2 short/DwFJO, DRw11, and DRw13 haplotypes. This latter functional determinant has never been described until now.