Octapeptide but not nonapeptide from HIV-1 p24gag protein upregulates cell surface HLA-C expression

Reciprocal recognition of an HLA-Cw4-restricted HIV-1 gp120 epitope by CD8+ T cells and NK cells

OBJECTIVES

The HIV-1 Nef protein selectively downregulates human leukocyte antigen (HLA)-A and HLA-B but not HLA-C molecules on the surface of infected cells. This allows HIV-infected cells to evade recognition by most cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. We investigated the recognition of an HLA-Cw4-restricted HIV-1 gp120 epitope SFNCGGEFF (SF9) and its variant SFNCGGEFL (SL9) by T cells and NK receptors.

DESIGN AND METHOD

Recognition of HIV-1 gp120 peptides (SF9 and SL9) by T-cell clones was measured by staining with HLA-Cw4-peptide tetrameric complexes and cytolytic assays using target cell pulsed with either peptides. KIR2DL1 binding to these two peptides was measured using surface plasmon resonance and tetramer staining of an NK cell line.

RESULT

: CTLs could recognize SF9 better than the variant SL9, as shown by both tetramer staining and cytolytic assays. Intriguingly, an HLA-Cw4 tetramer folded with the 'escape' variant SL9 could bind to KIR2DL1 on NK cell lines with higher affinity than HLA-Cw4-SF9. The binding of KIR2DL1 to its ligand results in inhibition of NK cell function. Our results indicate that the HIV-1 gp120 variant peptide SL9 could potentially escape both from NK cell and CTL recognition by increasing its affinity for KIR2DL1 binding.

CONCLUSION

These data suggest that HIV-1 can acquire mutations that are capable of escaping from both CTL and NK cell recognition, a phenomenon we have termed 'double escape'.

A novel trafficking signal within the HLA-C cytoplasmic tail allows regulated expression upon differentiation of macrophages

MHC class I molecules (MHC-I) present peptides to CTLs. In addition, HLA-C allotypes are recognized by killer cell Ig-like receptors (KIR) found on NK cells and effector CTLs. Compared with other classical MHC-I allotypes, HLA-C has low cell surface expression and an altered intracellular trafficking pattern. We present evidence that this results from effects of both the extracellular domain and the cytoplasmic tail. Notably, we demonstrate that the cytoplasmic tail contains a dihydrophobic (LI) internalization and lysosomal targeting signal that is partially attenuated by an aspartic acid residue (DXSLI). In addition, we provide evidence that this signal is specifically inhibited by hypophosphorylation of the adjacent serine residue upon macrophage differentiation and that this allows high HLA-C expression in this cell type. We propose that tightly regulated HLA-C surface expression facilitates immune surveillance and allows HLA-C to serve a specialized role in macrophages.

The contribution of HLA class I antigens in immune status following two doses of rubella vaccination

The variability of humoral and cellular immune responses modulated by human leukocyte antigen (HLA) genes is a significant factor in the protective effect of rubella vaccines. We performed HLA class I typing in a group of 346 healthy schoolchildren and young adults who previously received two doses of measles-mumps-rubella-II vaccine. Rubella virus-specific humoral (serum antibody) immunity and cell-mediated immunity (lymphocyte proliferation) were assessed. Median values for antibody levels and stimulation indices (SI) were 38.63 IU/ml and 2.29 IU/ml, respectively. The alleles that provided suggestive, but not conclusive, evidence of HLA association with rubella seropositivity were HLA-B*2705 (median, 24.68 IU/ml; p = 0.160), B*4501 (median, 61.22 IU/ml; p = 0.098), Cw*0303 (median, 30.34 IU/ml; p = 0.102) and Cw*0704 (median, 26.58 IU/ml; p = 0.144). These alleles approach, but do not achieve, statistical significance. Of all the alleles analyzed, HLA-B*3503 (median SI, 3.00; p = 0.031) and HLA-Cw*1502 (median SI, 3.19; p = 0.035) were positively associated with lymphoproliferative responses to rubella virus antigens, whereas the HLA-B*3901 (SI, 1.34; p = 0.066) allele was negatively associated. This suggests that class I HLA alleles may have limited associations with humoral and cellular immune responses to rubella vaccine. These data may facilitate our understanding of immune response variation in a genetically outbred heterogeneous population.