Zeta CD20 Antibody. Zeta’s recombinant mouse antibody recognizes CD20, a non-Ig differentiation antigen of B cells and the expression of CD20 is restricted to normal and neoplastic B cells, being absent from all other leukocytes and tissues. CD20 is the most specific B-cell marker used in paraffin immunohistochemistry. CD20 acts as calcium channel involved in B cell activation and cell cycle progression.