This review focuses on how immunogens trapped by FDC In the form of Ag‐Ab complexes productively signal B cells. In vitro, Ag‐Ab complexes are poorly immunogenic but m vivo immune complexes elk ii potent recall responses. FDC trap Ag‐Ab complexes and make immune complex mated bodies or “iccosomes”. B cells endocytose iccosomes, the Ag is processed, and T‐cell help is elicited. In vitro, addition of FDC bearing appropriate Ag‐Ab complex to memory T and B cells provoke potent recall responses (IgG and IgE). FDC also provide nonspecific costimulatory signals which augment B‐cell proliferation and Ab production. B cell‐FDC contact is important and interference with ICAM‐1‐LFA‐1 interactions reduces FDC‐mediated costimulation. Preliminary data suggest that a costimulatory signal may be delivered via CRZL on FDC binding CR2 on B cells. FDC can also stimulate B cells to become chemotactically active and can protect lymphocytes from apoptosis. FDC also appear to be rich in that groups and may replace reducing compounds such as 2 mercaptoethanol in cultures. In short, FDC‐Ag specifically signals B cells through BCR, and FDC provide B cells with iccosomal‐Ag necessary for processing to elicit T i ell help. In addition, FDC provide nonspecific signals that are important to promote B‐cell proliferation, maintain viability, and induce chemotactic responsiveness.