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False-Positivity of HIV-2 Immunoblots in a Cohort of Elite Suppressors Infected With HIV-1

McKellar, Mehri S MD; Jongthavorn, Pam CRNP; Khanlou, Homayoon MD

JAIDS Journal of Acquired Immune Deficiency Syndromes: 15 April 2008 - Volume 47 - Issue 5 - p 644
doi: 10.1097/QAI.0b013e31815bacfa
Letters to the Editor

AIDS Healthcare Foundation, Los Angeles, CA

To the Editor:

Infection with HIV-2, the second causative etiology for AIDS, is mainly present in West Africa, with a slow spread to other continents. Compared with HIV-1 infection, the course of HIV-2 infection is associated with slower progression to AIDS, most likely attributable to lower plasma viral loads observed in these patients.1 In dual-infected patients, control of HIV-1 may be associated with the ability to respond to HIV-2 gag epitopes and to maintain HIV-specific CD4 T-cell responses.2

We recently tested a small group of long-term nonprogressors with HIV-1 infection (elite suppressors) to rule out coinfection with HIV-2. Three of 13 patients underwent testing with an HIV-2 enzyme immunoassay (EIA), and all 13 had HIV-2 Immunoblots performed at VircoMed Laboratories/Laboratory Corporation of America (Minnetonka, MN). One of the 13 patients had a significant HIV-2 risk factor with a previous sexual partner from West Africa of unknown HIV status.

Using the commercially available assays, specimens were considered positive for the HIV-2 Immunoblot test if the gp36 band (env) was present. All patients tested positive with the HIV-2 EIA and the HIV-2 Immunoblot (of whom 2 were weakly positive). When HIV-2 qualitative polymerase chain reaction (PCR) tests were performed, all patients were negative, thus ruling out coinfection with HIV-2.

Although previous studies have reported high sensitivity (91% to 100%) and specificity (81% to 100%) for HIV-2 antibody testing,3 this may become more challenging in coinfected patients because of cross-reactivity. The 2 viruses have similar morphology and cell tropism, with homology exhibited in the conserved genes, such as the core proteins (gag) and reverse transcriptase (pol), and in other less conserved envelope (env) genes.3,4 Although qualitative PCR testing is available at reference laboratories, quantitative viral loads are not available except in research facilities.

Given the high false-positivity rate of the commercially available assays because of cross-reactivity with HIV-1, serologic testing for HIV-2 infection should be used only in patients with negative HIV-1 Western blot test results in areas in which HIV-2 is not endemic. In cases when dual infection is suspected, our recommendation would be to proceed directly to HIV-2 PCR testing.

Mehri S. McKellar, MD

Pam Jongthavorn, CRNP

Homayoon Khanlou, MD

AIDS Healthcare Foundation Los Angeles, CA

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REFERENCES

1. MacNeil A, Sankale JL, Meloni S, et al. Long-term intrapatient viral evolution during HIV-2 infection. J Infect Dis. 2007;195:726-733.
2. Zheng N, McElrath M, Sow P, et al. Role of HIV-specific T-cell immunity in the control of dual HIV-1 and HIV-2 infection. J Virol. 2007;81:9061-9071.
3. Malone J, Sheffield J, Tribble D, et al. Evaluation of three rapid/simple tests for detection of HIV-2 antibodies. J Acquir Immune Defic Syndr. 2000;23:281-283.
4. Kanki P. Epidemiology and natural history of human immunodeficiency virus type 2. In: Devita V, Hellman S, Rosenberg S, eds. AIDS: Etiology, Diagnosis, Treatment and Prevention. Philadelphia: Lippincott-Raven Press; 1997;127-135.
© 2008 Lippincott Williams & Wilkins, Inc.