Agreement study between two laboratories of immunofluorescence as a confirmatory test for human immunodeficiency virus type 1 antibody screening

Immunofluorescence assay in India for confirmation of HIV-1 infection using a T-cell line infected with defective HIV-1

BACKGROUND

In India, the enzyme immunoassay (EIA)/rapid test is used for screening and confirmatory antibody testing of HIV infection, and all HIV reactive samples are further confirmed by two other rapid tests working on different principles; however, Western blotting (WB) and immunofluorescence (IF) assays are not routinely performed in this country.

METHODS

A total of 2104 sera from Indian subjects were tested for the presence of HIV-1 antibody using EIA/rapid tests, according to the guidelines of the National AIDS Control Organization of India, and were also subjected to IF test using L-2 cells persistently infected with defective HIV-1. WB and a nested reverse transcriptase polymerase chain reaction (RT-PCR) were performed on discrepant samples.

RESULTS

IF results were 100% concordant with EIA/rapid tests for 212 HIV-1-positive samples and 1889 HIV-1-negative samples. Interestingly, three (0.14%) samples negative by EIA/rapid tests were weakly or moderately positive (1+/2+) by IF test. All three of these samples were confirmed to be negative by WB (reactive with Gag/Pol, but not with Env), but positive by RT-PCR with primers targeting the C2-V5 fragment of the env gene. These three samples were from individuals who voluntarily reported for HIV testing because of high-risk practices, and they may have been at an early stage of HIV infection.

CONCLUSIONS

These results confirm that the IF test using L-2 cells is a sensitive and specific alternative method for confirmation of HIV-1 infection and could be included in the diagnostic algorithm in reference laboratories in developing countries.

Efficiency of indirect immunofluorescence assay as a confirmatory test for the diagnosis of human retrovirus infection (HIV-1 and HTLV-I/II) in different at risk populations

We compared the indirect immunofluorescence assay (IFA) with Western blot (Wb) as a confirmatory method to detect antibodies anti retrovirus (HIV-1 and HTLV-I/II). Positive and negative HIV-1 and HTLV-I/II serum samples from different risk populations were studied. Sensitivity, specificity, positive, negative predictive and kappa index values were assayed, to assess the IFA efficiency versus Wb. The following cell lines were used as a source of viral antigens: H9 ( HTLV-III b); MT-2 and MT-4 (persistently infected with HTLV-I) and MO-T (persistently infected with HTLV-II). Sensitivity and specificity rates for HIV-1 were 96.80% and 98.60% respectively, while predictive positive and negative values were 99.50% and 92.00% respectively. No differences were found in HIV IFA performance between the various populations studied. As for IFA HTLV system, the sensitivity and specificity values were 97.91% and 100% respectively with positive and negative predictive values of 100% and 97.92%. Moreover, the sensitivity of the IFA for HTLV-I/II proved to be higher when the samples were tested simultaneously against both antigens (HTLV-I-MT-2 and HTLV-II-MO-T). The overall IFA efficiency for HIV-1 and HTLV-I/II-MT-2 antibody detection probed to be very satisfactory with an excellent correlation with Wb (Kappa indexes 0. 93 and 0.98 respectively). These results confirmed that the IFA is a sensitive and specific alternative method for the confirmatory diagnosis of HIV-1 and HTLV-I/II infection in populations at different levels of risk to acquire the infection and suggest that IFA could be included in the serologic diagnostic algorithm.

Kinetics study of human retrovirus antigens expression in T lymphocytic cell lines by indirect immunofluorescence assay

Indirect immunofluorescence assay (IFA) is a well-accepted assay for the confirmation of human retrovirus infection. Fluctuations in HIV-1 antigen expression in infected E-B2 cells depending on several factors have been reported. Cells kept in log phase expressed the highest levels of viral antigen. Thus, we studied the time kinetics of IFA positivity in MT-2 (HTLV-I), MO-T (HTLV-II), CEM, and H9 (HIV-1) cell lines. Uninfected T cell line, HT, was used as nonspecific control. Reference HTLV-I/II and HIV-1 serum panels from the Centers for Disease Control and Prevention (CDC) were tested by conventional IFA procedure on slides of each cell line made on different days. On the second day after subculture, HTLV-I strongly positive sera reacted on MT-2 and MO-T cells with a bright pericytoplasmic fluorescence pattern. Weakly positive sera showed a faint staining from the fifth day on, when all the sera showed the highest degree of fluorescence. With HIV-1 cell lines, sera predominantly reacted with a diffuse cytoplasmic pattern, although some sera showed a granular and pericytoplasmic capping staining. The highest degree of fluorescence was found at 3-5 days after subculture. We demonstrated that the sensitivity of the IFA for the detection of antibodies against human retroviruses depended on the day when the slides were assayed and on the serum antibody titer. The fifth day was the most appropriate for HTLV-I/II and HIV-1/H9 systems, whereas for HIV-1/CEM, the fourth day was better. Furthermore, the intensity of the immunofluorescence pattern differed with the antibody titers and the level of antigens expressed on the four cell lines studied. The IFA, improved in our laboratory, proved to be very sensitive, specific, and rapid and could be used as a supplementary/confirmatory assay for retrovirus infection.

Evaluation of an indirect immunofluorescence assay for confirmation of human immunodeficiency virus type 1 antibody in U.S. blood donor sera

An indirect immunofluorescence assay (IFA) was evaluated as a confirmatory test for antibody to human immunodeficiency virus type 1 in U.S. blood donor sera previously found to be repeatedly reactive by enzyme immunoassay. IFA results were 100% concordant with a licensed Western blot (immunoblot) for 53 negative and 49 positive samples. Four samples which exhibited antibody to viral proteins from more than one gene, yet were indeterminate by Western blot by the manufacturer's criteria, were also reactive by IFA, whereas 49 additional indeterminate samples were IFA negative.

Advantages of a human immunodeficiency virus type 1 (HIV-1) persistently infected HeLa T4+ cell line for HIV-1 indirect immunofluorescence serology

A HeLa T4+ cell line persistently infected with human immunodeficiency virus type 1 (HIV-1) was used in an indirect immunofluorescent antibody assay (IFA) system to explore its potential suitability as an alternative source of viral antigen for confirmatory IFA in HIV serology. In a study of 121 serum samples chosen because they were reactive on repeat examination by enzyme immunoassay but nonspecific by IFA by using HIV-1-infected H9 cells (H9 IFA) or gave discrepant results by enzyme immunoassay and H9 IFA, the specificity and sensitivity of the HeLa T4+ IFA were comparable to those of Western blot (immunoblot), and identification of the true positive samples among these discrepant or nonspecific samples by HeLa T4+ IFA was approximately twice that by H9 IFA. The primary advantages of using the HeLa cell line rather than lymphoid cell lines in IFA are that cells can be grown as a monolayer and that the individual cells are much larger. The cell membrane, cytoplasm, and nucleus are easily discernible; this allows specific and nonspecific staining to be distinguished. At least eight different nonspecific nuclear and cytoplasmic staining patterns were identified in this study by using T4+ cells.