Final answer:
C4b2a and C3bBb interact with C5 by cleaving it into C5a and C5b, which are crucial for the immune response, including cell lysis and inflammation.
Step-by-step explanation:
The interaction between C4b2a or C3bBb (convertase complexes of the complement system) and C5 leads to the cleavage of C5 into two fragments, C5a and C5b. This cleavage is an essential step in the activation of the latter stages of the complement cascade which play roles in the immune response, such as cell lysis through the formation of the membrane-attack complex (MAC) and facilitating inflammation and phagocytosis through chemotactic and opsonizing effects. C5a is an anaphylatoxin with potent inflammatory properties, while C5b initiates the assembly of the MAC. The correct answer to the student's question on how C4b2a and C3bBb interact with C5 is therefore 'b) Cleavage into C5a and C5b'.