Enhanced antibody activity in serum depleted of antigen

Presence of antigen and antibodies in a sample may interfere with the antibody, as well as with antigen detection assays. In such a situation, avidity of the probing antigen or antibody plays the key role in the assay. In the present study, using monoclonal antibodies against a mycobacterial antigen, lipoarabinomannan, patient serum is depleted of mycobacterial antigen by capture immunoradiometric assay and this antigen-depleted serum is tested for anti-lipoarabinomannan antibodies by inhibition immunoradio-metric assay. It is observed that serum, after depletion of antigen, revealed enhanced antibody activity compared to initial levels. It, therefore, appears that the avidity of the probing monoclonal antibody may detach the antigen from the loosely attached complexes and renders the complexed antibody free, thus increasing the reactive antibody molecules in the serum.