Influence of HLA-DR on the phenotype of CD4⁺ T lymphocytes specific for an epitope of the 16-kDa α-crystallin antigen of Mycobacterium tuberculosis

Abstract

T helper phenotype may be influenced by cytokine milieu, the differential expression of co-stimulatory molecules, antigen dose and by differences in affinity at the TCR-peptide-MHC interface. We investigated the latter hypothesis by examining the response of six HLA-DR-restricted CD4⁺ T cell lines specific for the immunodominant and permissively recognized p91-110 epitope of the 16-kDa α-crystallin protein of Mycobacterium tuberculosis. Each line was generated from a sensitized HLA-DR-heterozygous donor and all proliferated when peptide was presented by autologous irradiated peripheral blood mononuclear cells. However, when HLA-DR-matched homozygous Epstein-Barr-virus-transformed B cell lines (L-BCL) were used as peptide-presenting cells there was heterogeneity in the response. The most pronounced proliferative response and the highest IFN-γ secretion and cytolytic activity was stimulated by L-BCL expressing molecules (DRB1*0101, *1501 and *0401) with high affinity (IC₅₀ < 10 μM) for the 16p91-110 peptide. By comparison, IL-4 secretion or a lower proliferative response could occur when peptide was presented by alleles of high, or of intermediate (10 μM < IC₅₀ < 100 μM), affinity. These data support the hypothesis that the host MHC can influence CD4⁺ phenotype and have implications for subunit vaccination against tuberculosis.