Diagnostics

SEROLOGY TESTS FOR THE DIAGNOSTICS OF HTLV-I AND HTLV-II INFECTIONS

The serum samples are extracted for the anti-HTVL-I antibody using 2 authorized immunoenzymatic tests from different manufacturers, prepared with HTLV-I antigens from the total lisado of the virus and some recombinant proteins. These tests vary in sensibility to detect antibodies for the HTLV-II (4,5). Initially, the reagent samples are retested in duplication in order to minimize the possibility of a technical error on the reactivity. Specimens that are reagent in any one of the duplicated tests are considered repeatedly reagents. Specimens, which do not react in either one of the tests repeated in duplication, are considered non-reagents (3).

Recently, HTLV-I, HTLV-II, and gp21e recombinant antigens were incorporated to the ELISA, improving the specificity and the sensibility. Additional tests, such as the Immunoblot (WB) and the radioimmunoprecipitation assay, are necessary for interpreting, with correction, the specimens repeatedly reagents. Such additional tests should be capable to identify antibodies for the HTLV-I/II core protein (gag) and the envelope protein (env).

Indirect Immunofluorescence Assay (IFA) for HTLV-I/II antibodies was conducted in some laboratories. None of the additional assays was authorized by the FDA, but they are available in research institutions, blood banks, some public health care laboratories, industrial laboratories, and as "in house" tests in some diagnostics laboratories.

The following criteria for HTLV-I/II seropositive were adopted by a teamwork at the United States Public Health Services (USPHS) in 1988 (3): a specimen, which is repeatedly ELISA reagent for HTLV-I/II, has to demonstrate immnunoreactivity to protein p24 and to a product of the envelope gene (gp61/68 and/or gp46). The reagent serums are considered indeterminate if they do not meet these criteria but show immunoreactivity to at least one product. It could be required Immunoblot and Radioimmunoprecipitation assays to determine whether a specimen is positive or undetermined.

Serum specimens without immunoreactivity for any HTLV gene product, in more specific additional tests, are considered false-positives. Several studies, involving provirus amplification, support the precision of these diagnostic criteria. The people considered infected are those whose specimens meet the positive criteria for HTLV-I or HTLV-II (7,70).