Factors affecting suppressor cell activity in tumor-allosensitized mice

Area of Science:

• Immunology
• Tumor immunology
• Cellular immunology

Background:

• P-815 mastocytoma cells induce splenic suppressor cells in C57BL/6 mice.
• Suppressor cells play a role in regulating immune responses to tumors.

Purpose of the Study:

• To investigate the development and characteristics of splenic suppressor cells following allogeneic tumor sensitization.
• To determine the role of the thymus in the generation of these suppressor cells.
• To characterize the suppressor factor released by these cells.

Main Methods:

• Induction of P-815 mastocytoma in adult C57BL/6 mice.
• Assay of splenic suppressor cells in mixed lymphocyte cultures.
• Neonatal thymectomy in mice to assess the thymus's role.
• Analysis of suppressor factor release and characteristics.

Main Results:

• Suppressor cells appeared earlier and were more active after low-dose tumor sensitization, preceding cytotoxic activity.
• Higher tumor doses led to simultaneous appearance of suppressor and cytotoxic activity.
• Suppressor cells were not H-2 restricted but showed enhanced activity with specific alloantigen.
• Neonatal thymectomy abrogated suppressor cell development, indicating thymic origin of precursor cells.
• Suppressor factor (SF) release was enhanced by specific alloantigen and T-cell enrichment; SF was not H-2 restricted or antigen-specific.

Conclusions:

• The thymus is essential for generating splenic suppressor cell precursors after tumor allosensitization.
• Splenic suppressor cells and their factors contribute to immune regulation in tumor-bearing hosts.
• The timing of suppressor and cytotoxic cell activity depends on tumor dose, suggesting differential regulation.