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Macrophages in lymphoid organs are in close contact to nerve terminals of the sympathetic nervous system. Hence, these cells could be targets of neuronal modulation. We studied sympathetic neurotransmitters as chemoattractants enabling the aggregation of macrophages and nerve terminals. Norepinephrine (NE), neuropeptide Y (NPY), isoproterenol (beta-adrenergic), p-aminoclonidine (alpha2-adrenergic), methoxamine (alpha1-adrenergic), and adenosine triphosphate (ATP) were used to study human monocyte and macrophage migration in 48-well Boyden chambers. NE stimulated chemotaxis of monocytes and macrophages at an optimal concentration of 10-(10) M (P < 0.025). Isoproterenol, but not p-aminoclonidine or methoxamine, induced chemotaxis of monocytes (10(-10) M, P < 0.05). In these studies, elevation of cAMP is a critical step in NE-induced chemotaxis of monocytes. NPY (10(-11) M, P < 0.05) stimulated monocyte chemotaxis as well. ATP at 10(-4) and 10(-5) M stimulated undirected cell mobility (P < 0.05). All tested neurotransmitters of the sympathetic nerve terminal were potent chemoattractants. These findings may explain the close association of nerves and macrophages in tissue and lymphoid organs and may thus be of functional relevance in neuroimmunomodulation.

Maturation of cells of the mononuclear phagocyte lineage from bone marrow precursors to tissue macrophages (MAC) via circulating blood monocytes (MO) is a multistep process only partially understood. Similarly, MAC differentiation can be observed if MO are cultured in vitro. In an attempt to further characterize molecular changes occurring during this process we carried out differential screening of a MO-derived MAC cDNA library using MO and MAC cDNA. After subcloning and confirmation by a second round of screening, partial sequencing of 41 cDNA clones was performed. In 33 clones the sequences of 7 different previously identified cDNAs were found. The mRNA expression of two of the corresponding genes (apolipoprotein E, ferritin light chain) is already known to be up-regulated during MAC maturation. For one gene (cathepsin B), a specific up-regulation of mRNA expression could be shown corresponding to previous protein data. For four genes [human cartilage glycoprotein (HC-gp39), osteopontin, type IV collagenase, and tryptophanyl-tRNA synthetase] the specific expression in MAC versus MO was previously unknown but could be confirmed by the use of Northern blot analysis. Of these genes, HC-gp39 is especially interesting because it is only expressed during the late stages of MAC differentiation.

Functional competence as well as phenotype heterogeneity of macrophages depend on the completion of their maturation pathway. Differentiation of committed myeloid progenitor cells is induced by colony-stimulating factors (CSF), but no consistent data exist on which factor(s) induce the terminal maturation from the circulating blood monocyte to the mature macrophage. In vitro, monocyte to macrophage transformation occurs in the presence of serum and can be followed by the expression of the maturation-associated antigens gp65-MAX.1, gp68-MAX.3, and CD51. We describe that the differentiation-inducing activity in serum cannot be replaced by any of the known and available purified recombinant cytokines. In the absence of serum monocytes die in suspension cultures while surviving as non-differentiating cells when cultured adherent to plastic. In serum-free suspension cultures survival can be significantly improved by the addition of recombinant human macrophage (rhM)-CSF whereas other cytokines do not. At any stage of serum-free adherent culture, monocyte to macrophage differentiation can be induced rapidly by the addition of serum, whereas cytokines (rhM-CSF, recombinant human granulocyte macrophage [rhGM]-CSF, recombinant human granulocyte [rhG]-CSF, recombinant human interleukin [rhIL]-1, rhIL-3, rhIL-4, rhIL-6, tumor necrosis factor [TNF]-alpha, interferon [IFN]-alpha, IFN-gamma) alone or in combination are not effective. Serum-induced maturation, however, was suppressed in the presence of neutralizing anti-M-CSF antibodies. In addition to phenotype analysis, the secretory repertoire of rhM-CSF cultured monocytes was analyzed in comparison to serum cultured monocytes which further characterized them to be immature cells, i.e., low release of maturation-associated products such as alpha-2-macroglobulin, neopterin, fibronectin, and TNF-alpha, but high IL-6 secretion, an attribute of blood monocytes. We conclude that for monocyte survival in vitro the presence of endogenous M-CSF and possibly other autocrine factors elicited by cell adherence are required for the induction of macrophage maturation; however, yet undefined additional factor(s) are necessary. They are present in serum and may act in conjunction with M-CSF but are distinct from all known cytokines. Our in vitro system may be useful in the screening and discovery of these serum factor(s).

Cells of the mononuclear phagocyte system arise from circulating blood monocytes. Upon emigration from the vasculature, monocytes differentiate into macrophages, a process that monocytes similarly undergo in vitro. We have established primary cultures from elutriated or adherence-purified blood monocytes and analyzed the antigenic modulation during monocyte to macrophage transformation, which could be followed by the expression of specific antigens and which required as yet unknown inducer signals present in the serum. It is shown that in the absence of serum monocytes only survive in vitro when cultured adherent to plastic but rapidly die in suspension culture. Starting at 0.5%, serum induced maturation dose-dependently, with the optimal concentration being 2 to 5%. Of those antigens not present on monocyte, the low-affinity Fc receptor (CD16), the alpha-chain of the vitronectin receptor (CD51), gp65-MAX.1, and gp68-MAX.3 were expressed only upon serum-induced macrophage differentiation, whereas the transferrin receptor (CD71), MAX.26, and to some degree also gp65-MAX.11 appeared to be independent of maturation and were also found on primary cultures of adherent monocytes under serum-free conditions. In addition, the rapid induction of HLA class II antigens (within 24 hr) was similar with and without serum, as was the continued high-density expression in long-term culture. The monocyte-specific CD14 antigen was down-regulated in the absence of serum but kept its level of expression on differentiated macrophages. In comparison, alveolar and peritoneal macrophages, respectively, differed in their antigenic phenotype: Alveolar macrophages expressed high HLA class II antigens but low CD14, whereas for peritoneal macrophages the opposite was found. Both interferon-gamma and -alpha suppressed macrophage maturation in vitro but had contrary effects on HLA class II and CD16 expression: Interferon-gamma up-regulated the two types of antigens, which, in contrast, were down-regulated by interferon-alpha.