Modulation of human lymphocyte functions by group A streptococci

Area of Science:

• Immunology
• Microbiology
• Cell Biology

Background:

• Pathogenic bacteria can modulate host immune responses.
• Understanding streptococcal component interactions with human immune cells is crucial.

Purpose of the Study:

• To investigate the in vitro reactivity of human mononuclear cells (MNC) to group A, B, C, and G streptococci.
• To compare the immune response elicited by different streptococcal groups and their cellular components.

Main Methods:

• Incubation of heat-inactivated streptococci and isolated cellular components with MNC from healthy donors' peripheral blood and tonsils.
• Assays for DNA synthesis, leukocyte migration inhibitory factor (LIF) production, immunoglobulin (Ig) secretion, and plaque-forming cell (PFC) responses.
• Cocultivation studies to assess suppressor cell activity.

Main Results:

• Group A streptococcal cells, cell walls, and membranes stimulated DNA synthesis, LIF production, and Ig secretion in MNC.
• Tonsil MNC showed higher proliferation and PFC responses to group A streptococci than blood MNC.
• Group A streptococcal components induced polyclonal B lymphocyte activation, dependent on T cells and monocytes, similar to pokeweed mitogen.
• Precultured MNC and T cells, in the presence of group A streptococci, suppressed responses of fresh MNC, mimicking Concanavalin A-induced suppressor cells.
• Group B, C, and G streptococcal components did not activate lymphocytes.

Conclusions:

• Cellular components of group A streptococci possess potent polyclonal activating and suppressor-inducing properties on human mononuclear cells.
• These properties are specific to group A streptococci, as other groups failed to elicit similar responses.
• The findings highlight the immunomodulatory capacity of group A streptococci, involving T cell and monocyte cooperation.