Immunomodulation by Histoplasma capsulatum products; polyclonal activation and mitogenic effects

Area of Science:

• Immunology
• Microbiology

Background:

• Histoplasma capsulatum filtrate (histoplasmin) is known to modulate immune responses.
• Understanding its effects on lymphocyte populations is crucial for its clinical and immunological implications.

Purpose of the Study:

• To investigate the immunomodulatory effects of histoplasmin on non-immunized BALB/c mice.
• To characterize the nature of reactive spleen cells and their activation status post-histoplasmin inoculation.

Main Methods:

• Mice were inoculated with histoplasmin and monitored for spleen cell reactivity to sheep red blood cells (SRBC) over 21 days.
• Rosette-forming cell (RFC) assays were performed, including complement-mediated B-cell elimination.
• Lymphocyte proliferation assays were conducted using histoplasmin, LPS, and concanavalin A.

Main Results:

• Histoplasmin induced polyclonal activation of spleen cells, evidenced by increased anti-SRBC RFCs and enhanced responses to other erythrocytes.
• Both T- and B-lymphocytes were identified as erythrocyte-binding cells.
• Histoplasmin demonstrated dose-dependent immunosuppression when administered before SRBC, but this was reversible.
• Significant mitogenic activity of histoplasmin was observed on spleen, bone marrow, and thymus lymphocytes.

Conclusions:

• Histoplasmin acts as a potent polyclonal activator and mitogen for lymphocytes.
• It exhibits complex immunomodulatory effects, including dose-dependent immunosuppression.
• These findings highlight the significant biological activity of histoplasmin on the immune system.