THE PERIPHERAL-BLOOD FIBROCYTE IS A POTENT ANTIGEN-PRESENTING CELL CAPABLE OF PRIMING NAIVE T-CELLS IN-SITU

Recent studies have identified a novel population of blood-borne cells , termed fibrocytes, that have a distinct cell surface phenotype (coll agen(+)/CD13(+)/CD34(+)/CD45(+)), rapidly enter sites of tissue injury , and synthesize connective tissue matrix molecules, We found by flow cytometry that purified human fibrocytes express each of the known sur face components that are required for antigen presentation, including class II major histocompatability complex molecules (HLA-DP, DQ, and - DR), the costimulatory molecules CD80 and CD86, and the adhesion molec ules CD11a, CD54, and CD58, Human fibrocytes induced antigen-presentin g cell-dependent T cell proliferation when cultured with specific anti gen and this proliferative activity was significantly higher than that induced by monocytes and nearly as high as that induced by purified d endritic cells, Mouse fibrocytes also were found to express the surfac e components required for antigen presentation and to function as pote nt APCs in vitro. Mouse fibrocytes pulsed in vitro with the HIV-protei ns p24 or gp120 and delivered to a site of cutaneous injury mere found to migrate to proximal lymph nodes and to specifically prime naive T cells. These data suggest that fibrocytes play an early and important role in the initiation of antigen-specific immunity.