FIG. 2.

Increased help for Ab production mediated by CD1-restricted Th or NKT cells. In this model, we propose the following. (i) DCs capture protein, glycolipids, or complexes and subsequently present Ag in the context of CD1d to CD1d-NKT cells or present MHC class II to MHC class II-restricted Th cells. DCs therefore prime NKT and Th cells for further activation by Ag-presenting B cells. (ii) B cells capture Ag via a specific BCR to facilitate presentation to DC-primed NKT and/or Th cells. (iii) The T cell is stimulated via cognate interactions to produce IL-4 and to increase receptor engagement between the T cell and the B cell. (iv) The cytokine environment combined with receptor-mediated help stimulates Ab production. In this model, the relative contribution of MHC class II- and CD1-restricted help may depend on the relative affinity of glycolipid and peptide Ag for the T-cell receptor (TCR). Whether CD1- and MHC class II-restricted T cells interact directly to affect Ab production is not known.