Dipeptide uptake: a novel marker for testicular and ovarian macrophages

Testicular and ovarian macrophages seem to be involved in paracrine regulation of steroidogenesis. Markers suitable for the identification of these cells under viable conditions would allow new experimental approaches in the study of biological interactions between hormone-producing cells and tissue macrophages.

Dipeptide uptake was studied in primary cultures from rat testis and ovaries with the fluorescent dipeptide derivative beta-Ala-Lys-N epsilon-aminomethylcoumarin acetic acid (AMCA). Fluorescence microscopic studies revealed that the reporter peptide accumulated specifically in testicular macrophages, which were identified by subsequent immunostaining with the OX-42 antibody. In the ovarian cultures, however, transport of the fluorescence-labeled dipeptide was observed in cells that exhibited the morphological characteristics of macrophages but did not show positive immunoreactivity against the antibody employed. In both cases, dipeptide accumulation was blocked by the addition of Tyr-Gly, thus indicating that transport was not due to endocytosis. Competition studies performed with primary cultures from testis have shown that di-and tripeptides effectively reduce uptake of the tracer peptide, whereas compounds without an alpha- or beta-amino group, such as captopril and benzylpenicillin, do not.

These results indicate that the testicular and ovarian macrophages are equipped with a dipeptide transport system. The selective accumulation of the fluorescent dipeptide derivative beta-Ala-Lys-N epsilon-AMCA in testicular and ovarian macrophages permits the identification of these cell types under viable conditions.