Detection of anti-tat antibodies in CSF of individuals with HIV-associated neurocognitive disorders

Abstract

Despite major advances in the development of antiretroviral therapies, currently available treatments have no effect on the production of HIV-Tat protein once the proviral DNA is formed. Tat is a highly neurotoxic and neuroinflammatory protein, but its effects may be modulated by antibody responses against it. We developed an indirect enzyme-linked immunosorbent assay and measured anti-Tat antibody titers in CSF of a well characterized cohort of 52 HIV-infected and 13 control individuals. We successfully measured anti-Tat antibodies in CSF of HIV-infected individuals with excellent sensitivity and specificity, spanning a broad range of detection from 10,000 to over 100,000 relative light units. We analyzed them for relationship to cognitive function, CD4 cell counts, and HIV viral load. Anti-Tat antibody levels were higher in those without neurocognitive dysfunction than in those with HIV-associated neurocognitive dysfunction (HAND) and in individuals with lower CD4 cell counts and higher viral loads. We provide details of an assay which may have diagnostic, prognostic, or therapeutic implications for patients with HAND. Active viral replication may be needed to drive the immune response against Tat protein, but this robust immune response against the protein may be neuroprotective.

Fig 1

Relative Light Units of an ELISA for anti-Tat antibodies detected in spinal fluid of HIV-infected individuals without dementia (HIV-Normal) (MSK 0) (n=15; 86.7% > mean+1SD), with mild cognitive impairment (HIV-MCMD) (MSK 0.5–1) (n=20; 70% > mean+1SD), with moderate cognitive impairment (HIV-HAD) (MSK≥2) (n=17; 82.4% > mean+1SD), HIV negative controls (n=5), and neuro-inflammatory controls (n=8). Anti-Tat levels in spinal fluid of all HIV groups are significantly higher than in controls. The points in the figure represent individual patient data and lines represent the mean. Statistical analysis was by ANOVA, with Newman-Keuls post-test.

Fig 2

Detection of Antibodies to Tat in the CSF of individuals infected with HIV: (A) Relative Light Units of an ELISA for anti-Tat antibodies detected in spinal fluid of HIV-infected individuals without dementia (HIV-Normal) (MSK 0) (n=15; 86.7%>mean+1SD), with HIV-associated neurocognitive disorder (HAND) (MSK≥0.5) (n=37; 83.8%>mean+1SD), HIV negative controls (n=5), and neuro-inflammatory controls (n=8). Anti-Tat levels in spinal fluid of the HIV-Normal group were significantly higher than in HIV-HAND (p<0.05). Antibody level was significantly higher in HIV-infected individuals without dementia than the HIV negative individuals (p<0.01) and the neuro-inflammatory control individuals (p<0.001). CSF anti-Tat levels are higher in individuals with higher serum and CSF viral loads and lower CD4 cell counts. (B) In the CSF of individuals with HIV (n=51), anti-Tat levels are significantly higher in the group with serum viral load >400 copies/ml (p<0.01). (C) In the CSF of individuals with HIV (n=47), anti-Tat levels are significantly higher in the group with CSF viral load >400 copies/ml (p<0.01). (D) In the CSF of individuals with HIV (n=51), anti-Tat levels are significantly higher in the group with CD4 cell level <250 cells/μl (p<0.05). In all panels, the points in the figure represent individual patient data and lines represent the mean. Statistical analysis was by ANOVA with Newman-Keuls post-test for (A) and by unpaired t-test for (B, C, D).