Complement-dependent cellular cytotoxicity due to alternative pathway C3 activation by the target cell membrane

Area of Science:

• Immunology
• Cell Biology
• Complement System

Background:

• Cytotoxic activity of lymphocytes is crucial for immune surveillance.
• The role of serum components in modulating lymphocyte-mediated cytotoxicity is not fully understood.
• Interferon (IFN) is known to activate immune cells.

Purpose of the Study:

• To investigate the effect of human serum (HS) on lymphocyte cytotoxicity against Raji cells.
• To explore the influence of interferon (IFN) and serum components on this cytotoxic activity.
• To elucidate the role of the complement system, specifically C3, in lymphocyte-mediated killing.

Main Methods:

• Cytotoxicity assays using human blood lymphocytes and Raji cells.
• Inclusion of human serum (HS), hypogammaglobulinemic serum (HyS), heat-inactivated serum, and C3-depleted serum.
• Treatment of effector cells with interferon (IFN).
• Treatment of target Raji cells with IFN and assessment of lysis sensitivity.

Main Results:

• Human serum (HS) significantly augmented lymphocyte cytotoxicity against Raji cells.
• Interferon (IFN) activation of lymphocytes also enhanced cytotoxicity.
• C3-depleted serum was inefficient in augmenting cytotoxicity, suggesting C3's involvement.
• IFN treatment of Raji cells reduced their lysis sensitivity, an effect reversed by HS.

Conclusions:

• Human serum, particularly through C3 activation and deposition on target cells, facilitates lymphocyte recognition and lysis.
• These findings suggest a mechanism for the natural killing phenomenon involving complement activation.
• Serum components and IFN play significant roles in modulating cellular immune responses.