No abstract

SUMMARYWe compared the immunological functions of interferon-c (IFN-c)-induced, classically activated macrophages (caMW) and of interleukin-4 (IL-4)-and glucocorticoid-induced, alternatively activated macrophages (aaMW) in a human co-culture system in vitro. Proliferation of peripheral blood leucocytes (PBL) or CD4+ T cells mediated by optimal doses of phytohaemagglutinin (PHA) or concanavalin A (Con A) was only marginally influenced by caMW, but was strongly inhibited by aaMW. The degree of lymphocyte proliferation sustained in the presence of caMW was gradually reduced in a dose-dependent fashion by the addition of aaMW. Flow cytometric analysis revealed that expression of costimulatory molecules such as CD11a, CD40, CD54, CD58, CD80 and CD86 did not vary significantly between caMW and aaMW and was low for CD58, CD80 and CD86. As shown by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, IL-10 was expressed in caMW, aaMW and control macrophages; the level of expression of IL-10 was slightly enhanced in aaMW. Neither neutralizing anti-IL-10 antibodies, indomethacin nor NG-monomethyl--arginine (NMMLA) was able to reverse aaMW-mediated inhibition of lymphocyte proliferation. Of several agents interfering with various second messenger pathways, cAMP and the Ca2+-ionophor A23187 inhibited differentiation of cultured human monocytes into phenotypically mature aaMW expressing MS-1 high molecular weight protein (MS-1-HMWP) and RM 3/1 antigen, and prevented the suppressive action of aaMW on lymphocyte proliferation. In conclusion, these results show that aaMW actively inhibit mitogen-mediated proliferation of PBL and CD4+ T cells independently of the expression of costimulatory molecules and of IL-10, NO or prostaglandin synthesis, and that inhibition of phenotypic differentiation of aaMW is paralleled by a lack of functional maturation. Thus, fully matured aaMW may be functional in down-regulating CD4+ T-cell-mediated immune reactions by an as yet unknown mechanism.