Human T cell derived, cell-bound complement iC3b is integrally involved in T cell activation.

Area of Science:

• Immunology
• Complement System Biology
• T cell Activation

Background:

• The complement system is crucial for immunity, but its direct impact on T cell responses is increasingly recognized.
• Research on complement component 3 (C3) fragments' effects on human T cells is limited, with most studies focusing on animal models.

Purpose of the Study:

• To investigate the production and function of C3 fragments on activated human T cells.
• To elucidate the interaction between human T cell-derived C3 fragments and dendritic cells.

Main Methods:

• Analysis of C3 fragment production on anti-CD3 activated human T lymphocytes from blood and tonsil.
• Investigation of T cell-derived iC3b binding to dendritic cell receptors (CR3/CR4) in an allogeneic system.
• Assessment of C3a receptor (C3aR) and C3a binding on activated T cells.

Main Results:

• Activated human T cells produce C3, with iC3b being the predominant fragment on their surface.
• T cell-bound iC3b interacts with CR3 and CR4 receptors on dendritic cells, significantly enhancing T cell proliferation.
• No detectable C3a or C3aR binding was observed on activated human T cells.

Conclusions:

• Human T cells actively participate in complement regulation by producing C3 fragments like iC3b.
• The iC3b-CR3/CR4 interaction on dendritic cells is a key mechanism for enhancing human T cell proliferation.
• Unlike in mice, the C3a peptide likely does not directly mediate T cell activation in humans.