Langerhans cells do not express alternative macrophage activation-associated CC chemokine (AMAC)-1.

We have cloned a novel human CC chemokine, alternative macrophage activation-associated CC chemokine (AMAC)-1 that is highly homologous to macrophage inflammatory protein (MIP)-1alpha. In contrast to MIP-1alpha, AMAC-1 is induced in macrophages by Th2-associated cytokines IL4, IL13, and IL10 in vitro; in addition, AMAC-1 is expressed by Th1-suppressive alveolar macrophages in vivo. Surprisingly, however, AMAC-1 is also expressed by GM-CSF-induced, in vitro monocyte-derived dendritic cells when treated by IL4. Here, we present a detailed analysis of AMAC-1 expression in monocyte-derived dendritic cells in vitro and show that the prime dendritic cells in vivo, i.e. epidermal Langerhans cells, do not express AMAC-1 mRNA. In conclusion, AMAC-1 is a novel CC chemokine whose Th2-associated expression pattern in alternatively activated suppressor macrophages in vivo and in vitro and its absence from epidermal Langerhans cells in vivo suggest that it may be involved in inhibition of Th1 reactions and in tolerance induction.

Alternative macrophage activation-associated CC-chemokine-1, a novel structural homologue of macrophage inflammatory protein-1 alpha with a Th2-associated expression pattern.

We have cloned a novel human CC-chemokine, alternative macrophage activation-associated CC-chemokine (AMAC)-1. The isolated cDNA clone (803 bp) shows a single open reading frame of 267-bp coding for 89 amino acid residues; mature AMAC-1 protein is predicted to consist of 69 amino acids with a m.w. of 7855. Sequence alignment and 3D-modeling show the typical structural characteristics of CC-chemokines with special features in the receptor-activating domain. AMAC-1 is most closely related to MIP-1 alpha with a cDNA and protein sequence homology of 55% and 59%, respectively. However, the expression pattern of AMAC-1 is directly opposite to that of MIP-1 alpha. While MIP-1 alpha is induced by classical macrophage mediators such as LPS and is inhibited by IL-4 and glucocorticoids, AMAC-1 is specifically induced in macrophages by alternative macrophage mediators such as IL-4, IL-13, and IL-10. Expression of AMAC-1 is inhibited by IFN-gamma while glucocorticoids exert a slightly positive synergistic effect in combination with IL-4. Peripheral blood monocytes do not express AMAC-1; time course experiments show that monocyte-to-macrophage differentiation is a prerequisite for AMAC-1 expression. Expression of AMAC-1 by granulocyte-macrophage CSF/IL-4-induced, monocyte-derived dendritic cells is complex; in mature adherent dendritic cells, however, only minor AMAC-1 mRNA expression was found. In vivo, AMAC-1 is expressed by alveolar macrophages from healthy persons, smokers, and asthmatic patients. In conclusion, AMAC-1 is a novel CC-chemokine whose expression is induced in alternatively activated macrophages by Th2-associated cytokines; thus, AMAC-1 may be involved in the APC-dependent T cell development in inflammatory and immune reactions.

Alternatively activated macrophages actively inhibit proliferation of peripheral blood lymphocytes and CD4+ T cells in vitro.

We compared the immunological functions of interferon-gamma (IFN-gamma)-induced, classically activated macrophages (caM phi) and of interleukin-4 (IL-4)- and glucocorticoid-induced, alternatively activated macrophages (aaM phi) 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 caM phi, but was strongly inhibited by aaM phi. The degree of lymphocyte proliferation sustained in the presence of caM phi was gradually reduced in a dose-dependent fashion by the addition of aaM phi. Flow cytometric analysis revealed that expression of costimulatory molecules such as CD11a, CD40, CD54, CD58, CD80 and CD86 did not vary significantly between caM phi and aaM phi and was low for CD58, CD80 and CD86. As shown by reverse transcriptase-polymerase 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 antibodies, indomethacin nor NG-monomethyl-L-arginine (NMMLA) was able to reverse aaM phi-mediated inhibition of lymphocyte proliferation. Of several agents interfering with various second messenger pathways, cAMP and the Ca(2+)-ionophore A23187 inhibited differentiation of cultured human monocytes into phenotypically mature aaM phi expressing MS-1 high molecular weight protein (MS-1-HMWP) and RM 3/1 antigen, and prevented the suppressive action of aaM phi on lymphocyte proliferation. In conclusion, these results who that aaM phi 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 aaM phi is paralleled by a lack of functional maturation. Thus, fully matured aaM phi may be functional in down-regulating CD4+ T-cell-mediated immune reactions by an as yet unknown mechanism.