A nucleoprotein peptide of influenza A virus stimulates assembly of HLA-B27 class I heavy chains and β₂-micro-globulin translated in vitro

Abstract

MOST cytotoxic T lymphocytes (CTL) recognize epitopes of foreign viral proteins in association with class I major histo-compatibility complex (MHC) molecules¹. Viral proteins synthesized in the cytoplasm require intracellular fragmentation and exposure to the class I antigens for the development of CTL responses^2–4. Although indirect evidence for binding of peptides to class I antigens has accumulated, direct binding has only been shown recently^5,6. The formation of complexes between peptide and class I antigen may occur in the endoplasmic reticulum (ER)^7,8 and peptides have been shown to induce assembly of the class I complex⁹. We have translated the messenger RNAs encoding HLA-B27 (subtype 2705)^10,11 and 02-microglobulin in a rabbit reticulocyte lysate supplemented with human microsomal membranes (to mimic ER membranes), in the absence and presence of a peptide derived from the nucleoprotein¹² (residues 384–394) of influenza A virus. This peptide induces CTL activity against target cells expressing the HLA-B27 antigen¹³. Here we report direct evidence that the nucleoprotein peptide promotes assembly of the HLA-B27 heavy chain and β₂-microglobulin, and that this can occur in the ER immediately after synthesis of the two proteins.