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  • Title: IgA testing for diagnosis of retroviral infections in the Caribbean.
    Author: Ridel PR, Artus JC, Capron A.
    Journal: Bull Pan Am Health Organ; 1991; 25(3):201-6. PubMed ID: 1742565.
    Abstract:
    In Guadeloupe, a Caribbean island with a high prevalence of HTLV-I infected subjects, the percentage of false positive results for HIV IgG is high, requiring additional time and expense for confirmatory tests. This article describes a simple way of overcoming this problem. First, all IgG and IgG immune complexes are removed by protein G treatment, and then IgA enzyme-linked immunosorbent assay (ELISA) and the Western blot test are performed with minor modification of commercially available kits. Researchers wanted to determine whether they could do a more specific ELISA HIV test directed at IgA rather than IgG antibodies. So they 1st used streptococcal protein G to remove IgG from serum samples of 10 follow up patients from Guadeloupe who previously tested positive via ELISA for HIV-1/2 IgG and HTLV-I IgG. They did this to test sera for IgA. The protein G treatment resulted in a 99.9% reduction in the IgG concentration (12.21.7 mg/ml to .007-.017 mg/ml). After IgG depletion, the researchers noted no ELISA positive samples for HIV-1/2 or HTLV-I IgG. In fact, all the values were well below the cutoff levels. This result indicated that streptococcal protein G treatment followed by IgA ELISA is more specific than testing for IgG. The sera of 8 patients tested negative for HIV-1/2 IgA, but all tested positive for HTLV-1 IgA. This result showed that IgA may be more useful than IgG for also confirming retroviral infections. The sera of 2 patients were 44% and 27% above the cutoff level indicating that these patients had HIV-1/2 IgA antibodies. The researchers observed that protein G treatment suppressed all HIV-1/2 and HTLV-I IgG Western blot reactivity which confirmed the effectiveness of protein G treatment. Further the HIV IgG bands in the 8 false positive sera did not materialize at all suggesting that the IgG reactivity observed was most likely nonspecific. These results indicated that nonspecific HIV-1/2 IgG caused the false positive HIV-1/2 IgG ELISA results. In conclusion, in Caribbean countries where HTLV-1 infection can be as high as 13%, the more specific HIV IgA ELISA test should be used since its use saves time and money. Further it can do generalized testing for HTLV antibodies.
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