<prompt> Which subtype of IgG activates alternate complement system.IgGlIgG2IgG3IgG4  <response>: Ans. id d i.e. IgG4 Four subclasses oflgG are there with IgG is found in greatest amount and IgG4 in least amount.IgG,-65IgG3-8IgG2-23IgG4-4 Ig G1, Ig G3 and sometimes Ig G2 activate classical complement pathway. Ig G4 activates alternate complement pathway. IgG2 is directed against polysaccharide antigen so it is important in defence against encapsulated bacteria. 