Major histocompatibility complex class I-restricted alloreactive CD4+ T cells

Abstract

Although it is well established that CD4+ T cells generally recognize major histocompatibility complex (MHC) class II molecules, MHC class I-reactive CD4+ T cells have occasionally been reported. Here we describe the isolation and characterization of six MHC class I-reactive CD4+ T-cell lines, obtained by co-culture of CD4+ peripheral blood T cells with the MHC class II-negative, transporter associated with antigen processing (TAP)-negative cell line, T2, transfected with human leucocyte antigen (HLA)-B27. Responses were inhibited by the MHC class I-specific monoclonal antibody (mAb), W6/32, demonstrating the direct recognition of MHC class I molecules. In four cases, the restriction element was positively identified as HLA-A2, as responses by these clones were completely inhibited by MA2.1, an HLA-A2-specific mAb. Interestingly, three of the CD4+ T-cell lines only responded to cells expressing HLA-B27, irrespective of their restricting allele, implicating HLA-B27 as a possible source of peptides presented by the stimulatory MHC class I alleles. In addition, these CD4+ MHC class I alloreactive T-cell lines could recognize TAP-deficient cells and therefore may have particular clinical relevance to situations where the expression of TAP molecules is decreased, such as viral infection and transformation of cells.

Figure 1

CD4⁺ T-cell lines proliferate in response to T2-B27 (a T2-cell line transfected with HLA-B*2705). (a) Proliferation is expressed as Δ counts per minute (c.p.m.) of CD4⁺ T-cell lines to a panel of B27⁺ and B27⁻ stimulator cell lines. Data shown are the means of duplicate wells ± standard deviation (SD). (b) Flow cytometric analysis of the phenotype of the six T2-B27-reactive T-cell lines.

Figure 2

Responses to T2-B27 (a T2-cell line transfected with HLA-B*2705) are CD4 dependent. Proliferative responses are displayed as Δ counts per minute (c.p.m.) to T2-B27 in the presence or absence of a blocking monoclonal antibody (mAb) specific for CD4. Data shown are the means of triplicate results ± standard deviation (SD).

Figure 3

Differential responses to T2-B27 (a T2-cell line transfected with HLA-B*2705) on reconstitution of TAP molecules. Proliferative responses, displayed as Δ counts per minute (c.p.m.) of the CD4⁺ T-cell lines to T2, T2-B27 and T2-B27-TAP (T2-B27 reconstituted with TAP1 and TAP2). Data shown represent the mean values of triplicate wells ± standard deviation (SD).

Figure 4

Inhibition of responses to T2-B27 (a T2-cell line transfected with HLA-B*2705) by major histocompatibility complex (MHC) class I-specific monoclonal antibodies (mAbs). Proliferative responses, displayed as Δ counts per minute (c.p.m.), to T2-B27 in the presence or absence of 10 µg/ml of the MHC class I-specific mAb, W6/32, the human leucocyte antigen (HLA)-B27-specific mAb, ME1, the free heavy chain-specific mAb, HC10, the HLA-DR-specific mAb, L243, and the HLA-A2-specific mAb, MA2.1. Data shown are the means of triplicate wells ± standard deviation (SD).

Figure 5

Proliferative responses are observed to the Epstein–Barr virus-transformed lymphoblastoid cell line (EBV-LCL) by three of the major histocompatibility complex (MHC) class I-reactive CD4⁺ T-cell lines. Proliferative responses are expressed as Δ counts per minute (c.p.m.) to a panel of EBV-LCL. Proliferative responses to T2-B27 (a T2-cell line transfected with HLA-B*2705) are shown as a control. Data shown represent the mean values of triplicate results.