What part of C1q does antibody bind with?

The antibody binds with the globular heads of C1q. C1q is a component of the complement system and plays a crucial role in the activation of the classical complement pathway. The structure of C1q includes a large molecule with multiple globular heads that can interact with the Fc region of antibodies (specifically IgG and IgM) that are bound to antigens.

When antibodies attach to their respective antigens, the Fc regions become available to interact with C1q. This binding is an essential trigger for the complement cascade, leading to opsonization of pathogens, recruitment of inflammatory cells, and ultimately, clearance of immune complexes. Therefore, the globular heads of C1q are specifically designed to recognize and bind to these antibody Fc regions, initiating a series of immune responses. This interaction illustrates the intricate connections between the adaptive and innate immune systems, highlighting the critical role of antibodies in complement activation.