Quantification of immunofluorescence on individual erythrocytes coated with varying amounts of antigen

Quantification of the parameters in an antigen—antibody fluorescent reaction in which it was possible to vary the amount of the antigen, was carried out in a model system. Formalinized erythrocytes were coated with different amounts of ¹³¹I-labelled human IgM. The cells were then exposed to fluorescein-conjugated antiserum to human IgM. The fluorescence intensity of individual cells was measured with a microspectrofluorimeter. As the cells were coated with varying amounts of protein it was possible to investigate the relationship between the quantity of protein antigen and the intensity of fluorescence.

Reactivity of radioiodinated serum antibody from Burkitt's lymphoma and nasopharyngeal carcinoma patients against culture lines derived from Bukrkitt's lymphoma

The IgG serum immunoglobulin fraction of two Burkitt's lymphoma (Mutua and Kiliopa) and one African nasopharyngeal carcinoma patient (Kipkoech) was conjugated to iodine-131 (¹³¹I). It is known from previous studies with fluorescein labelled conjugates that all three sera contain antibody against the Epstein–Barr virus (EBV)-associated membrane antigen complex, present on the surface of lymphoblastoid cells in EBV-carrier cultures. All three radioiodinated conjugates attached to live cells of an EBV-carrying Burkitt line (Maku), but not to EBV-free Raji cells. A Swedish control serum (Berith) did not block the binding of any of the three conjugates, whereas unconjugated sera of Mutua, Kiliopa and Kipkoech showed various degrees of blocking and cross-blocking. The blocking patterns were in good agreement with previous tests, performed with the same sera against their fluorescein conjugated derivatives.

Antibody release tests, involving preincubation of live cells with one of the three conjugates, followed by incubation with unlabelled serum revealed a certain `hierarchy' between the three sera with regard to their ability to displace radioiodinated surface-coupled immunoglobulin. This ability could be related to the competitive behaviour of the same sera in the cross blocking tests. The results are believed to reflect differences in the affinity of the three antibodies, due either to differences in fit in relation to the surface antigen(s) carried by the Maku target cell, or to differences in the duration of immunization in the three patients.