The complement system is a crucial part of the innate immune system. When activated, complement proteins are cleaved into smaller and larger fragments, each with specific functions.

Complement Component Fragmentation

Understanding the fragmentation of key complement proteins is essential:

• C3 Cleavage: The central component C3 is cleaved by C3 convertase into two fragments:
  • C3a (smaller fragment): Acts as an anaphylatoxin, promoting inflammation.
  • C3b (larger fragment): Acts as an opsonin (promotes phagocytosis) and is essential for forming the C5 convertase.
• C2 Cleavage: C2 is cleaved by the C1 complex (classical/lectin pathways) or C3b (alternative pathway) into two fragments:
  • C2b (smaller fragment): Has enzymatic activity but is often considered less significant than C2a in forming convertases.
  • C2a (larger fragment): Combines with C3b to form the C5 convertase (specifically, the classical/lectin pathway C3 convertase is C4b2a, where 'a' denotes the larger fragment of C2).

Identifying Larger Fragments

Based on the fragmentation process:

• C3b is the larger fragment derived from C3.
• C2a is the larger fragment derived from C2.

Therefore, the larger fragments among the given options are C3b and C2a.

Conclusion

The complement components that are larger fragments are C3b and C2a. This corresponds to options B and C.