CD8α² CD11b⁺ Dendritic Cells Present Exogenous Virus-like Particles to CD8⁺ T Cells and Subsequently Express CD8α and CD205 Molecules

Recombinant porcine parvovirus virus-like particles (PPV-VLPs) are particulate exogenous antigens that induce a strong, specific cytotoxic T lymphocyte (CTL) response in the absence of adjuvant. In the present report, we demonstrate in vivo that dendritic cells (DCs) present PPV-VLPs to CD8⁺ T cells after intracellular processing. PPV-VLPs are captured by DCs with a high efficacy, which results in the delivery of these exogenous antigens to 50% of the whole spleen DC population. In vivo, a few hours after injection, PPV-VLPs are presented exclusively to CD8⁺ T cells by CD8α⁻ DCs, whereas 15 hours later they are presented mainly by CD8α⁺ DCs. After PPV-VLPs processing, a fraction of CD11b⁺ DCs undergo phenotypic changes, i.e., the up-regulation of CD8α and CD205 and the loss of CD4 molecules on their surface. The failure to detect mRNA coding for CD8α in CD11b⁺ DCs suggests that CD8α expression by these cells is not due to de novo synthesis. In recombination-activating gene knockout mice (Rag^−/−), CD11b⁺ DCs did not express CD8α and PPV-VLPs presentation by CD8α⁺ DCs was severely diminished. These results indicate that both CD8α⁻ and CD8α⁺ DCs play an important role in the induction of CTL responses by exogenous antigens, such as VLP.