Diagnostics

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

In contrast, people whose samples are "indeterminate" rarely are infected with any one of the viruses (70,71). There are rare cases of people, with reactivity for p19 and for an envelope gene (gp61/68 and/or gp46) product, but with no signs of reactivity for p24, who were considered infected by the HTLV-I/II (72). An important step toward serologic tests for HTLV was the development of a recombinant protein of the envelope p21e. Reactivity for p21e (ELISA and WB) was considered highly sensible for the HTLV-I/II infection, and it was observed in almost 100% of the infected individuals (73). However, the specificity of the p21e reactivity was questioned (74,75).

For the purposes of notification and counseling, the positivity of the samples which shows p21e serologically should be confirmed by tests capable of identifying the reactivity for the envelope, such as radioimmunoprecipitation or assays based in recombinant proteins (76), or through PCR, until additional information can become available. The additional serologic tests, discussed above, are thus incapable of differentiating HTVL antibodies from those of the HTLV-II. The relative intensity of the reactivity for the mordaça p19 proteins and p24 in the Immunoblot to differentiate HTLV-I from HTLV-II (77) was applied, but such differentiation could be incorrect (78). Recently, several synthetic peptides and recombinant proteins were developed for this purpose (8,9,79).

Thus, like the additional tests previously discussed, all these tests are applied in research only. Preliminary data indicates that they can be highly specified in order to differentiate the HTLV-I antibodies from those of the HTLV-II (8,9,79). Not all HTVL-I/II-positive serum specimens can be differentiated as HTLV-I or HTLV-II, applying these tests. In these cases, more sophisticated methods, such as the provirus amplification or virus insulation, are necessary to differentiate the HTLV-I from the HTLV-II infection. Up to this moment, the WB is one of the confirmation tests more applied for HTLV-I and II (WB HTLV 2.4, Genelabs, USA), which uses recombinant proteins specific to the HTLV-I and HTLV-II, plus one truncated region from the gp21 (GD21), besides proteins common to both viruses.

Therefore, the positivity criterion takes place when the serum reacts against the core protein (gp19 OR p24), GD21, the recombinant specific to the HTLV-I (RGP46-I), or the recombinant specific to the HTLV-II (RGP46-II). Any other pattern on the bands is considered inconclusive, or when it does react to the RGP46-I or RG-46-II, but there is the presence of the GD21, as the HTLV-I/II (Figure 1).