The significance of the macrophage content of human tumours.

The effective localization of an immunogenic rat sarcoma (HSBPA) is related to its macrophage content. In order to infiltrate this tumous with macrophages, T-cell function is important. In a tumour of low immunogenicity, MC3, with a low macrophage content, thymectomy has little effect on the ease with which such a tumour metastasizes. The monocytes in the peripheral blood of a rat myeloid leukaemia are of host origin and are significantly raised during the growth of the leukaemia. Similar monocytoid cells are found in human acute myelogenous leukaemias and appear to be important in the prognostic features of this type of leukaemia. The origin of these monocytoid cells has not been elucidated. In 56 solid human tumours the macrophage content of metastatic tumours is low (less than 10%) whereas the range in primary or locally recurrent tumours is 0-30%. It is too early to say whether the low macrophage infiltrated primary will readily metastasize compared to the high macrophage containing tumour.