Generation of in vitro natural cytotoxicity of horse lymphocytes against sarcoid-derived tumor cells not expressing major histocompatibility complex antigens.

The research article is about an investigation into the immune response of horse lymphocytes to sarcoid tumor cells. The researchers found that the horse lymphocytes showed a natural defense mechanism that preferentially targets and destroys tumor cells lacking surface expression of major histocompatibility complex antigens, without the need for conventional T-cell receptors or antibodies.

Methods

• The researchers analyzed the immune responses of lymphocytes from horses with sarcoid tumors by studying the proliferative responses using a mixed lymphocyte tumor cell culture (MLTC) assay and testing lymphocyte-mediated cytotoxicity against various horse target cells.
• The study utilized 12 horses with sarcoid tumors and 15 control horses. Lymphocytes from the horse blood were cocultured in the MLTC with various types of cells including sarcoid cells, equine testis cells, and normal equine dermal fibroblasts.
• These lymphocytes were then tested for proliferative responses using a method called [3H]thymidine uptake and cytotoxicity against the same targets was assessed using a 51Cr release assay.
• The lymphocyte populations were also analyzed for common surface markers.

Results

• The results showed that lymphocytes from horses with sarcoids exhibited a unique proliferative response in MLTC against Mc-1 cells. However, this protocol failed to generate cytotoxic lymphocytes.
• Exceptionally, lymphocytes cultured in a medium containing 10% allogeneic serum demonstrated selective natural cytotoxicity against Mc-1 that did not rely on DNA synthesis.
• About 80% of the lymphocytes disappeared during the culture process, however, the remaining viable lymphocytes showed a decrease in the number of CD4+ T lymphocytes, while the numbers of T cells with receptors for a molecule called Helix pomatia A hemagglutinin remained constant.
• A minimal number of lymphocytes displayed Fc-receptors for IgG, were complement-reactive positive cells, or were B cells expressing surface immunoglobulin.

Conclusion

• The findings suggest that a natural defense mechanism exists that can recognize and lyse (break down) tumor cells deficient in the surface expression of major histocompatibility complex antigens, without the intervention of conventional T-cell receptors or antibodies.
• This discovery could potentially provide new pathways for treatment strategies for horses with sarcoid tumors.