Phenotyping of immune cell infiltrates in breast and colorectal tumours

White cell infiltration of solid tumors is an important prognostic indicato r in malignant disease. Although macrophage infiltration is associated with good outcome in colorectal cancer, a high macrophage content is associated with poor prognosis in breast cancer. Suppressor macrophages prevent T cel l activation in normal tissues such as mucosal linings exposed to continuou s antigenic challenge. Interleukin 10 (IL-10), an immunosuppressive cytokin e, inhibits macrophage co-stimulation of T cells. Suppressor macrophage numbers, T cell numbers and T cell activation status were assessed in cell suspensions obtained from fresh specimens of breast a nd colorectal tumours and matched normal tissues. IL-10 production by both malignant and matched normal tissue was also assessed. This study identified elevated numbers of suppressor macrophages in breast tumors compared to matched normal breast tissue. Colorectal tumors did not contain significant numbers of these cells. Although T cell numbers are inc reased in breast tumors, these cells do not appear to be fully activated, a s assessed by major histocompatability complex class II and Interleukin 2 r eceptor expression. In contrast, T cells in colorectal tumors exhibit great er expression levels of these markers. Breast tumors produce significantly higher levels of IL-10 than normal breast tissue whereas IL10 levels in col orectal tumors are similar to normal colon tissue. Our findings of high suppressor macrophage numbers, high levels of IL-10 an d poorly activated T cells in breast tumors compared to low suppressor macr ophage numbers, low IL-10 and fully activated T cells in colorectal tumors may explain why high macrophage content is associated with poor prognosis i n breast cancer and good prognosis in colorectal malignancy.