Cutaneous immunization rapidly activates liver invariant Vα-14 NKT cells stimulating B-1B cells to initiate T cell recruitment for elicitation of contact sensitivity

T cell recruitment to elicit contact sensitivity (CS) requires a CS-initiating process mediated by B-1 cells that produce IgM, which activates complement to promote T cell passage into the tissues. We now show that Valpha14i NKT cells induce B-1 cell activation likely by releasing IL-4 early postimmunization. The CS initiation process is absent in Jalpha18(-/-) and CD1d(-/-) NKT cell-deficient mice and is reconstituted by populations enriched for Valpha14i NKT cells. Transfers are not effective if cells are derived from IL-4(-/-) mice. Staining with specific tetramers directly showed that hepatic Valpha14i NKT cells increase by 30 min and nearly double by 2 h postimmunization. Transfer of immune B-1 cells also reconstitutes CS responses in NKT cell-deficient mice. The B-1 cells act downstream of the Valpha14i NKT cells to restore CS initiation. In addition, IL-4 given systemically to Jalpha18(-/-) or CD1d(-/-) NKT cell-deficient mice reconstitutes elicitation of CS. Further, splenocytes from immune Jalpha18(-/-) mice produce less antigen (Ag)-specific IgM antibodies compared with sensitized WT mice. Together these findings indicate that very early after skin immunization Valpha14i NKT cells are stimulated to produce IL-4, which activates B-1 cells to produce Ag-specific IgM, subsequently needed to recruit effector T cells for elicitation of CS responses.