Age related differences in immunocompetence and incidence of mammary adenocarcinoma in murine mammary tumor virus-infected C3H/Bi mice.

In breeder C3H/Bi female mice, infected neonatally by murine mammary tumor virus (MTV), the incidence of spontaneous mammary tumors is greater than 95% between 5 and 9 months of age. In young (2-3 months) female the probability for developing a tumor in the next month is negligible, higher than 80% in mice of middle age (5-6 months) but lower than 4% in aged (10-12 months) females. The age-related changes of some immune functions of spleen cells from these tumor free female mice have been evaluated. While the proliferative capacity of cells to Phytohemagglutinin (PHA) increases, the T cell-dependent antibody response against sheep red blood cells (SRBC) and the antibody-dependent cellular cytotoxicity (ADCC) are significantly decreased in 5-6-month-old mice as compared to the young (2-3 months) female mice. The antibody response against SRBC and the mitogenic response to PHA decline markedly in 10-12-month-old mice but the ADCC increases in this group of mice. In addition, assays with monoclonal anti-Lyt-1 and anti-Lyt-2 antibodies indicate that percentage of Lyt 1- 2+ cells (suppressor and cytotoxic T cells) is lower in 10-12-month-old female as compared to 5-6-month-old animals. These results show that the immune alterations observed in 10-12-month-old C3H/Bi mice are not closely associated with an increase in incidence of spontaneous tumors and suggest that a high non-T killer cell activity could protect some of these older C3H/Bi female mice against mammary tumor development.