T helper cell-mediated interferon-gamma expression after human parvovirus B19 infection: persisting VP2-specific and transient VP1u-specific activity

Abstract

Human parvovirus B19 is a small non-enveloped DNA virus with an icosahedral capsid consisting of proteins of only two species, the major protein VP2 and the minor protein VP1. VP2 is contained within VP1, which has an additional unique portion (VP1u) of 227 amino acids. We determined the ability of eukaryotically expressed parvovirus B19 virus-like particles consisting of VP1 and VP2 in the ratio recommended for vaccine use, or of VP2 alone, to stimulate, in an HLA class II restricted manner, peripheral blood mononuclear cells (PBMC) to proliferate and to secrete interferon gamma (IFN-gamma) and interleukin (IL)-10 cytokines among recently and remotely B19 infected subjects. PBMC reactivity with VP1u was determined specifically with a prokaryotically expressed VP1u antigen. In general, B19-specific IFN-gamma responses were stronger than IL-10 responses in both recent and remote infection; however, IL-10 responses were readily detectable among both groups, with the exception of patients with relapsed or persisting symptoms who showed strikingly low IL-10 responses. Whereas VP1u-specific IFN-gamma responses were very strong among the recently infected subjects, the VP1u-specific IFN-gamma and IL-10 responses were virtually absent among the remotely infected subjects. The disappearance of VP1u-specific IFN-gamma expression is surprising, as B-cell immunity against VP1u is well maintained.

Fig. 1

Effect of HLA class I-specific (W6/32) and class II-specific (L243) monoclonal antibodies (mAbs) on B19-specific interferon (IFN)-γ (a) and interleukin (IL)-10 (b) responses. Background cytokine production (in the presence of corresponding blocking antibody) was subtracted from total to yield antigen-specific cytokine production. Subject groups: S3 is a healthy B19-seropositive, remotely infected ‘top responder’ having strong B19-specific T cell immunity. ‘C’ indicates recently infected patients. Note: patient C11 was pregnant, and had asymptomatic B19 infection and fetal death. Background IFN-γ responses were 0 pg/ml with or without mAbs, whereas backround IL-10 responses ranged 0–10, 0–8 and 0–7 pg/ml with ‘No Mab’, with W6/32 and with L243, respectively.