免疫学系知识库

Fragment 450650 of the spike (S) protein (S450650) of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) contains epitopes capable of being recognized by convalescent sera of SARS patients. Vaccination of mice with recombinant S450650 (rS450650) can induce Abs against SARS-CoV, although the titer is relatively low. In the present study, a fusion protein linking a fragment (residues 39272) of murine calreticulin (CRT) to S450650 in a prokaryotic expression system was created. Compared with target antigen alone, the recombinant fusion product (rS450650-CRT) has much improved hydrophilicity and immunogenicity. The S450650-specific IgG Abs of BALB/c mice subcutaneously immunized with rS450650-CRT were in substantially higher titer (approximately fivefold more). Furthermore, the fusion protein, but not rS450650 alone, was able to elicit S450650-specific IgG responses in T cell deficient nude mice. Given that rCRT/39272 can drive the maturation of bone-marrow-derived dendritic cells, directly activate macrophages and B cells, and also elicit helper T cell responses in vivo, we propose that fragment 39272 of CRT is an effective molecular adjuvant capable of enhancing target Ag-specific humoral responses in both a T cell-dependent and independent manner. Fusion protein rS450650-CRT is a potential candidate vaccine against SARS-CoV infection.