Human resident peritoneal macrophages: phenotype and biology

Summary . Macrophages represent the primary line of host defences in the peritoneal cavity. In order to study the metabolic activity and maturation stage of human resident peritoneal macrophages (PMo), peritoneal fluid (PF) was taken by Douglas puncture from healthy hyperstimulated infertile women undergoing oocyte retrieval for in vitro fertilization. Peritoneal fluid and macrophage culture fluids were studied for different inflammatory mediators such as interleukin-1 (IL-1), tumour necrosis factor (TNF) and interleukin-6 (IL-6). The level of macrophage colony-stimulating factor (M-CSF), which represents a macrophage proliferation and differentiation factor, was determined in the PF and in the serum. Furthermore, the macrophage phenotypic profile was analysed, in particular the expression of sex steriod hormone receptors. IL-1, IL-6 and TNF were detectable in the PF and in the culture supernatants of PMo whether stimulated or not by IFN-γ and LPS. The mean level of M-CSF in the PF was 6.37 ± 2.02 ng/ml as measured by RIA; this level did not correlate with the concentration of PMo. The mean PF-M-CSF level was 1.4-fold higher than in the sera as measured by a EIA. Oestrogen and progesterone receptors could not be demonstrated on the PMo analysed, so that a direct relationship between the ovarian steroid concentration in these women and the function of PMo was unlikely. As compared to peripheral blood monocytes (Mo), PMo showed a phenotypic profile, with some more mature features, e.g. increased expression of CD14, CD68, FcRII, FcRIII, CR3, CR4 and MHC class II determinants. These results indicate that resident PMo have acquired in vivo a certain differentiation and/or activation state under micro-environmental factors where cytokines secreted by the Mo themselves or by other cells such as the mesothelium may play important roles.