Biological Sex Influences Human Bystander CD8⁺ T Cell Activation

Area of Science:

• Immunology
• Infectious Diseases
• Sex Differences in Health

Background:

• COVID-19 outcomes show a significant sex bias, with males experiencing greater severity and mortality.
• Antigen-independent "bystander-activated" CD8+ T cells are implicated in the severity of viral infections like COVID-19.
• The influence of biological sex on bystander T cell activation remains largely unexplored.

Purpose of the Study:

• To investigate potential sex differences in bystander CD8+ T cell activation.
• To determine if biological sex impacts the magnitude of T cell responses independent of direct antigen stimulation.

Main Methods:

• Peripheral blood mononuclear cells (PBMCs) were isolated from age-matched male and female donors.
• Cells were stimulated with cytokines (IL-15, IL-12/18, IL-12/15/18) to induce bystander T cell activation.
• NKG2D expression, IFN-γ production, and antigen-independent cytotoxicity against tumor cells were measured.

Main Results:

• Male CD8+ T cells stimulated with IL-15 demonstrated enhanced bystander activation, evidenced by increased NKG2D expression and greater antigen-independent cytotoxicity.
• No significant sex differences were observed in bystander IFN-γ production following IL-12/18 or IL-12/15/18 stimulation.
• These findings suggest sex-specific regulation of CD8+ T cell effector functions.

Conclusions:

• Biological sex influences bystander CD8+ T cell activation, particularly in response to IL-15.
• Sex-based differences in T cell cytotoxicity may contribute to observed sex biases in viral disease severity.
• Further research is warranted to elucidate the mechanisms underlying these sex differences in immune responses.