ALTERNATIVELY ACTIVATED MACROPHAGES ACTIVELY INHIBIT PROLIFERATION OFPERIPHERAL-BLOOD LYMPHOCYTES AND CD4(-CELLS IN-VITRO() T)

We compared the immunological functions of interferon-gamma (IFN-gamma )-induced, classically activated macrophages (caM Phi) and of interleu kin-4 (IL-4)- and glucocorticoid-induced, alternatively activated macr ophages (aaM Phi) in a human co-culture system in vitro. Proliferation of peripheral blood leucocytes (PBL) or CD4(+) T cells mediated by op timal doses of phytohaemagglutinin (PHA) or concanavalin A (Con A) was only marginally influenced by caM Phi, but was strongly inhibited by aaM Phi. The degree of lymphocyte proliferation sustained in the prese nce of caM Phi was gradually reduced in a dose-dependent fashion by th e addition of aaM Phi. Flow cytometric analysis revealed that expressi on of costimulatory molecules such as CD11a, CD40, CD54, CD58, CD80 an d CD86 did not vary significantly between caM Phi, and aaM Phi and was low for CD58, CD80 and CD86. As shown by reverse transcriptase-polyme rase chain reaction (RT-PCR) analysis, IL-10 was expressed in caM Phi, aaM Phi and control macrophages; the level of expression of IL-10 was slightly enhanced in aaM Phi. Neither neutralizing anti-IL-10 antibod ies, indomethacin nor N-G-monomethyl-L-arginine (NMMLA) was able to re verse aaM Phi-mediated inhibition of lymphocyte proliferation. Of seve ral agents interfering with various second messenger pathways, cAMP an d the Ca2+-ionophor A23187 inhibited differentiation of cultured human monocytes into phenotypically mature aaM Phi expressing MS-1 high mol ecular weight protein (MS-1-HMWP) and RM 3/1 antigen, and prevented th e suppressive action of aaM Phi on lymphocyte proliferation. In conclu sion, these results show that aaM Phi actively inhibit mitogen-mediate d proliferation of PBL and CD4(+) T cells independently of the express ion of costimulatory molecules and of IL-10, NO or prostaglandin synth esis, and that inhibition of phenotypic differentiation of aaM Phi, is paralleled by a lack of functional maturation. Thus, fully matured aa M Phi may be functional in down-regulating CD4(+) T-cell-mediated immu ne reactions by an as yet unknown mechanism.