Which is the immunoglobulin which activates complement by alternate pathway?

The central process in the complement is the activation of C3 which is the major component of complement. In classical pathway, activation of C3 is achieved by C42 (C3 convease). The activation of C3 without the prior paicipation of C142 is known as alternate pathway. The first example of alternate pathway was that of properdin system as a group of serum proteins contributing to antimicrobial defence without requiring specific antibodies. The activator in this system was zymogen, a polysaccharide from the yeast cell wall, but many other substances can also be used to activate the pathway. Theses include bacterial endotoxins, IgA & D, cobra venom factor & nephritic factor. Ref: Ananthanarayanan & Paniker's microbiology 8th Ed Page 120.