CD40LG and chickenpox: Immunological binding between antigen and anti-B19 IgG antibodies was found to be specific as the standard graph [Figure 1] yielded a near sigmoid curve in the indirect in-house ELISA (qualitative) test and no cross-reactions were observed with sera taken from cases with viruses causing rash and similar clinical manifestations such as rubella, herpes simplex virus, varicella zoster, and Epstein Barr viruses, while it reacted specifically with serial sera taken from B19 infected cases and who were either anti-B19 IgM positive and anti-B19 IgG negative but seroconverted later on follow up.