Phagocytosis (effector functions of Ab)

When phagocytosis takes place, the cell membrane of the phagocyte adheres to the cell membrane of the Ag. There are many Ag that possess structures that interfere with this adherence. Examples of these structures are capsules. In this case, the immune system compensates. It does this by forming Ab, activating complement and using cell receptors. How does it do this? Lets begin
Firstly the immune system produces a specific Ab to the Ag. This becomes an immune complex. If the Ab is either IgG or IgM, the immune complex is capable of activating complement. Remember that C’ attaches to CH2 of IgG and CH3 of IgM. When C’ is activated, the cascade results in the formation of C3b which attaches to the cell membrane of the Ag and acts as a cell receptor or cell marker. This receptor interacts with CR1 and CR3 both of which are expressed by phagocytes. Round one to the immune system.
Secondly the Fc portion of the Ab can nad does interact with phagocytes via the Fc gamma receptor found on the phagocyte. Round two to the immune system.
Remember at the beginning the Ag was all excited because it had this capsule. It was jumping all around saying; ‘ha ha ha, I have a capsule and you can’t phagocytose me!’ now its game set and match in favour of the immune system. Immune system saves the day yet again!