Abstract
The kinetics of ‘sarcoma’ cell appearance and inflammatory cell infiltration into primary Moloney sarcoma virus (MSV)‐induced tumors has been studied in normal and partially immunosuppressed anti‐lymphocyte‐globulin (ALG)‐treated A/WySn mice. The ALG treatment facilitated an earlier appearance of gp70‐positive ‘sarcoma’ cells accompanied by an intense inflammatory response. Time course pulse‐labelling studies showed that a decreasing proportion of gp70‐positive ‘sarcoma’ cells were incorporating [^3^H]‐thymidine in vivo in both normal and immunosuppressed mice as the lesion progressed to maximum size. ALG‐treated mice inoculated with MSV were given a single injection of [^3^H]‐thymidine immediately prior to extensive appearance of gp70‐positive ‘sarcoma’ cells (day 6) and were studied for the presence of labelled gp70‐positive cells 2 h, 2 days and 6 days post labelling. The data indicate that few cells divided during the time in which an 8‐ to 10‐fold increase in virus‐positive ‘sarcoma’ cell number occurred. These experiments provide evidence that recruitment rather than proliferation of virus‐positive cells occurred. The results also suggest that, within the tumor, defense mechanisms develop which restrict sarcomacell proliferation also in ALG‐treated mice. The composition of inflammatory cells during the course of tumor progression and regression in the uncompromised mice revealed that the proportion of lymphocytes was highest early and late during tumor development, dropping to a minimum at the peak size of the tumor. Macrophages and granulocytes constituted 70–80% of the total cells recovered at peak tumor size and the onset of regression. In the ALG‐treated mice, the proportions of macrophages, granulocytes, and infrequent lymphocytes remained constant throughout the duration of the tumor progression. A decrease in total cells, including a decrease in gp70‐positive cells, was noticed before a change in the proportion of infiltrating lymphocytes occurred due to recovery of the immune system. The composition of the inflammatory cells at onset of regression suggests that macrophages and granulocytes are of major importance in the defense against MSV infection.