Antibodies against full-length Tat protein and some low-molecular-weight Tat-peptides correlate with low or undetectable viral load in HIV-1 seropositive patients.
BACKGROUND
The efficacy of a specific humoral response to transactivating Tat protein was studied in a group of HIV-1 seropositive drug addicts, who had previously received a similar course of anti-retroviral treatment with two reverse transcriptase inhibitors.


OBJECTIVE
The aim of the study was to evaluate the meaning of an immune response to Tat protein in HIV-1 seropositive patients with different levels of HIV-1 RNA viremia.


METHODS
The study analyzed the presence of anti-Tat antibody reacting either with full-length Tat or with individual overlapping Tat-peptides (Tat(6-14), Tat(11-24), Tat(36-50), Tat(46-60), Tat(56-70) and Tat(65-80)), in a group of HIV-1 seropositive subjects with different peripheral blood viral loads. Plasma samples were examined by immunoenzymatic assay for the presence of anti-Tat IgG antibody and for the quantification of peripheral blood (plasma) viral load by branched DNA assay.


RESULTS
The large majority of HIV-1 patients showed detectable levels of serum IgG to full-length-Tat, and the anti-Tat antibody level presented an inverse correlation with viral load magnitude. The analysis of antibody levels against individual overlapping Tat-peptides clearly showed that an undetectable viral load was significantly associated with the presence of a high antibody concentration against Tat(6-14), Tat(36-50) and Tat(46-60) (P=0.002, P=0.027 and P<0.001, respectively).


CONCLUSIONS
In HIV-1-infected patients, a strong humoral immune response against HIV-1 Tat protein is inversely correlated to peripheral blood viral load and, in particular, a high level of antibody against Tat peptides containing amino acid residues 6-14 (Tat(6-14)), 36-50 (Tat(36-50)) and 46-60 (Tat(46-60)) is associated with an undetectable plasma viral load. These findings may help to tailor anti-HIV-1 Tat-containing vaccines.
Department of Clinical and Experimental Medicine, Section of Microbiology, University of Bologna, Via Massarenti, 9-40138 Bologna, Italy. remc@med.unibo.it
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D000328:Adult; D019380:Anti-HIV Agents / Q000627:therapeutic use; D005260:Female; D015696:Gene Products, tat / Q000276:immunology*; D015483:HIV Antibodies / Q000097:blood*; D015658:HIV Infections / Q000097:blood / Q000188:drug therapy / Q000821:virology*; D006679:HIV Seropositivity / Q000097:blood / Q000821:virology*; D015497:HIV-1 / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification*; D006801:Humans; D007124:Immunoenzyme Techniques; D007074:Immunoglobulin G / Q000097:blood; D008297:Male; D010446:Peptide Fragments / Q000276:immunology; D012367:RNA, Viral / Q000032:analysis; D019562:Viral Load; D054322:tat Gene Products, Human Immunodeficiency Virus
D019380:Anti-HIV Agents; D015696:Gene Products, tat; D015483:HIV Antibodies; D007074:Immunoglobulin G; D010446:Peptide Fragments; D012367:RNA, Viral; C111139:Tat peptide (37-72), Human immunodeficiency virus 1; D054322:tat Gene Products, Human Immunodeficiency Virus; C415751:tat peptide (1-9), Human immunodeficiency virus 1; C109668:tat peptide (32-72), Human immunodeficiency virus 1