Question

Digestion of an immunoglobulin with pepsin yields F(ab′)2 fragments. Several clinical trials using F(ab′)2 fragments are being conducted for their use as blocking molecules. What is the immune phenomenon that is most likely to be seen with an F(ab′)2 fragment?

A. Complement fixation

B. Opsonization

C. Antigen neutralization

D. Immunoglobulin polymerization

E. React with Fc receptors

Answer 1

Option C.

Digestion with pepsin leads to degradation of Fc fragments and only the F(ab')2 fragment is recovered. F(ab')2 has intact antigen binding sites, and therefore, can bind with foreign antigen and result in antigenic neutralization. Since, the Fc portion is degraded, it can not carry out functions such as opsonization, complement fixation, immunoglobulin polymerization, reaction with Fc receptors, etc., all of which requires the presence of an intact Fc portion.