STUDY OF THE EFFECT OF GAMMA-IRRADIATION ON BOVINE SERUM SAMPLES ON THE ABILITY OF MONOCLONAL-ANTIBODIES TO DETECT INVARIANT ANTIGENS OF TRYPANOSOMA-CONGOLENSE, T-VIVAX AND TRYPANOSOMA-BRUCEI IN ENZYME-LINKED IMMUNOSORBENT ASSAYS

Samples of bovine serum from uninfected and African trypanosomes-infec ted animals were tested before and after gamma-irradiation, using thre e sandwich enzyme-linked immunosorbent assays (ELISA). Each test syste m utilized a different monoclonal antibody, reputedly allowing the spe cific detection of conserved-invariant cytoplasmic antigens of trypano nosomes, T. congolense, T. vivax, and T. brucei, respectively. Results have identified two groups of samples. The first contained samples wh ere there were unequivocal ELISA results indicating positivity and neg ativity, for nonirradiated samples. In this group, irradiation had no effect on the diagnostic sensitivity of the assays. All samples shown to be positive before irradiation remained positive and those shown to be negative, remained negative. There was, however, a statistically s ignificant reduction in signal in each of the ELISAs following irradia tion. The second group contained samples identified before irradiation as flanking the diagnostic negative/positive threshold of OD greater than or equal to 0.05. These showed a negative bias after irradiation of the order of OD -0.01, which was shown to be statistically signific ant by paired t-statistics. Without correction of the given diagnostic negative/positive threshold, bovine sera with OD values around the th reshold were expected to deliver more false negative test results upon irradiation. This was confirmed when serological data were compared w ith parasitological findings; where three times more false negative te st results were found from irradiated serum samples. Consequently, for this group of irradiated bovine samples tested by ELISA, the re-adjus tment of the diagnostic negative/positive threshold of the ELISAs usin g defined irradiated serum samples is recommended; otherwise, the freq uency of false negative results might be increased. (C) 1998 Elsevier Science B.V. All rights reserved.