Human skeletal myoblasts spontaneously activate allogeneic complement but are resistant to killing

Area of Science:

• Immunology
• Cell Biology
• Muscle Physiology

Background:

• The complement (C) system is implicated in muscle diseases.
• Human myoblasts and rhabdomyosarcoma cells are studied in relation to C activation.

Purpose of the Study:

• To investigate the spontaneous activation of the complement system by human myoblasts and rhabdomyosarcoma cell lines.
• To understand the mechanisms of complement resistance in myoblasts.
• To explore the implications of complement activation in muscle diseases and gene therapy.

Main Methods:

• Assessing complement activation via classical pathway in myoblasts and rhabdomyosarcoma cells.
• Quantifying the release of anaphylatoxins and C fragment deposition.
• Evaluating the role of complement regulatory molecules (MCP, CD59, DAF) and fluid-phase regulators (C1-inhibitor, factor H, C4BP, S-protein, clusterin).
• Investigating the effect of IFN-gamma and TNF-alpha on regulator expression.
• Testing the efficacy of soluble complement receptor I (sCR1) in protecting myoblasts.

Main Results:

• Human myoblasts and rhabdomyosarcoma cells spontaneously activate complement via the classical pathway.
• Cells release anaphylatoxins and are coated with opsonic C fragments but resist cell killing.
• Abundant expression of membrane (MCP, CD59) and fluid-phase complement regulators confers resistance.
• IFN-gamma and TNF-alpha enhance the expression of these regulators.
• Inhibition of complement with sCR1 protects myoblasts in vitro.

Conclusions:

• Spontaneous complement activation on myoblasts generates inflammatory mediators, potentially exacerbating muscle inflammation.
• Complement activation on myoblasts may affect gene delivery efficiency.
• Complement regulatory molecules are crucial for myoblast survival.
• sCR1 shows promise for treating C-mediated muscle diseases and improving gene delivery.