Comparison of cellular and secreted proteins of macrophages from the testis and peritoneum on two-dimensional polyacrylamide gels: evidence of tissue specific function.

It has been shown that the testis contains a population of cells with many characteristics typical of macrophages of other tissues. However, these macrophages are unique in that they secrete a product(s) that is responsible for stimulating testosterone secretion by Leydig cells while peritoneal macrophages have no similar effect. The purpose of the present study was to compare the pattern of cellular and secreted proteins of rat testicular macrophages to those of peritoneal macrophages using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Cellular and secreted proteins of cultured macrophages from the testis and peritoneum were labeled with 35S-methionine and 35S-cystine and then analyzed by 2D-PAGE using a computer-assisted image analysis system. It was found that the patterns of both cellular and secreted proteins of testicular macrophages were vastly different than those of peritoneal macrophages. One striking difference was the presence of a family of proteins in the 47 kd range, with a range of pI from 5.7-6.3 that represented approximately 57% of the total protein secreted by testicular macrophages. Proteins of similar molecular weight and pI represented only approximately 15% of the total peritoneal macrophage secreted proteins. Many other differences were observed in less abundant cellular and secreted proteins. These studies strongly support the concept that macrophages are functionally heterogeneous and secrete a group of proteins characteristic to the histological location of these cells.