Rachel L. Allen

Direct visualization of HIV-1-specific cytotoxic T lymphocytes during primary infection.

ObjectiveHIV-specific cytotoxic T lymphocytes (CTL) are believed to play an important role in containing viral replication throughout HIV-1 infection. Previous studies have attempted to quantify the HIV-1-specific CTL precursor frequency during primary HIV infection by using limiting dilution analysis, which almost certainly underestimates the true CTL frequency. Here we use a relatively new technique to quantify HIV-specific CD8 T cells in primary HIV infection. MethodsWe have used soluble tetrameric complexes of HLA class I molecules complexed with HIV epitope peptides to study the dynamics and frequency of HIV-specific CD8 T cells in relation to plasma viral load in early HIV infection, in three patients with a highly focused HIV-specific CTL response. ResultsWe show that the frequencies of HIV-1-specific CD8 T cells in acute infection are significantly higher than previously documented and can be demonstrated well before full seroconversion. These studies also confirm the immunodominance of the B27-restricted response in HIV infection and demonstrate a close temporal relationship between the numbers of circulating HIV-specific CD8 T cells and viral load. ConclusionsThese findings strongly suggest that HIV-1-specific CD8 T cells are responding directly to the level of viral replication in early HIV infection and are a major factor in its control. In addition, the data indicate that immunodominance for CD8 T-cell responses is established in the acute phase of HIV infection.

The role of HLA-B27 in spondyloarthritis

Abstractu2002The human major histocompatibility complex (MHC) class I allele HLA-B27 bears a striking association with the spondylolarthritic group of inflammatory arthritides, yet despite extensive studies its role in the disease process remains obscure. As an MHC class I protein, the primary function of HLA-B27 is to complex with β2-microglobulin forming a structure that presents short antigenic peptides for recognition by cytotoxic T lymphocytes (CTL). It has been proposed that the role of HLA-B27 in spondyloarthropathy involves this process of antigen presentation, and of the numerous theories proposed to explain the association, the most popular have involved the binding and presentation of arthritogenic peptides. Transgenic rodent studies directly implicate HLA-B27 heavy chains in disease pathogenesis, but suggest that the mechanism may be distinct from their primary function. The recent demonstration that HLA-B27 heavy chains can form stable homodimers may thus be of relevance. This review summarizes the evidence supporting current theories of disease association and proposes an alternative model of disease based on recent findings.

Importance of a conserved TCR J alpha-encoded tyrosine for T cell recognition of an HLA B27/peptide complex.

Human HLA B27‐restricted cytotoxic T lymphocytes (CTL) specific for the influenza A epitope NP383u2009–u2009391 use similar TCR α and β chains, with two closely related Jα segments used by six of nine CTL clones from three unrelated donors (Bowness et al., Eur. J. Immunol. 1993. 23: 1417u2009–u20091421). The role of TCR complementarity‐determining region (CDR)3α residues 93 and 100u2009–u2009102 was examined by site‐directed mutagenesis, following expression of the TCR α and β extracellular domains from one clone as a TCR ζ fusion heterodimer in rat basophil leukemia (RBL) cells. For the first time we have measured direct binding of tetrameric HLA B*2705/NP383u2009–u2009391 complexes to transfected TCR. Independently peptide‐pulsed antigen‐presenting cells (APC) were used to induce TCR‐mediated degranulation of RBL transfectants. Our results show a key role for the conserved TCRα CDR3 Jα‐encoded residue Y102 in recognition of HLA B27/NP383u2009–u2009391. Thus the Y102D mutation abolished both tetramer binding and degranulation in the presence of peptide‐pulsed APC. Even the Y102F mutation, differing only by a single hydroxyl group from the native TCR, abolished detectable degranulation. Further mutations F93A and S100R also abolished recognition. Interestingly, the N101A mutation recognized HLA B27/NP in functional assays despite having significantly reduced tetramer binding, a finding consistent with “kinetic editing” models of T cell activation. Modeling of the GRb TCR CDR3α loop suggests that residue Y102 contacts the HLA B*2705 α1 helix. It is thus possible that selection of germ‐line TCRAJ‐encoded residues at position 102 may be MHC driven.