Why are agglutinates not seen in warm type autoimmune hemolytic anemia?
Because the antibody is IgG. IgG is called incomplete antibody.
RBCs have a strong negative charge on their surface called zeta potential. So the shortest distance attainable between two RBCs is 18nm. IgM molecule has a large pemtameric structure, so it has a distance of 30 nm between two binding sites. Hence, it is able to agglutinate RBCs.
But the small IgG molecule has only 12 nm gap between two binding sites. So it can't bind to multiple RBCs and hence fails to agglutinate them.
So it just coats the RBCs, which is taken to spleen to be killed.
Thank you, Divya, for explaining this to us =)