Persistence of HIV-1 structural proteins and glycoproteins in lymph nodes of patients under highly active antiretroviral therapy

Abstract

Here we report a long-term persistence of HIV-1 structural proteins and glycoproteins in germinal centers (GCs) of lymph nodes (LNs) in the absence of detectable virus replication in patients under highly active antiretroviral therapy (HAART). The persistence of viral structural proteins and glycoproteins in GCs was accompanied by specific antibody responses to HIV-1. Seven patients during the chronic phase of HIV-1 infection were analyzed for the presence of the capsid protein (HIV-1p24), matrix protein (HIV-1p17), and envelope glycoproteins (HIV-1gp120/gp41), as well as for viral RNA (vRNA) in biopsy specimens from LNs obtained before initiation of therapy and during HAART that lasted from 5 to 13 months. In parallel, these patients were also monitored for viremia and specific anti-HIV-1 antibody responses to structural proteins and glycoproteins both before and during treatment. Before-therapy viral levels, as determined by RT-PCR, ranged from 3 x 10(3) to 6.3 x 10(5) copies of vRNA per ml, whereas during treatment, vRNA was under detectable levels (<25 copies per ml). The pattern of vRNA detection in peripheral blood was concordant with in situ hybridization results of LN specimens. Before treatment, vRNA associated with follicular dendritic cells (FDCs) was readily detected in GCs of LNs of the patients, whereas during therapy, vRNA was consistently absent in the GCs of LN biopsies of treated patients. In contrast to vRNA hybridization results, viral structural proteins and glycoproteins, evaluated by immunohistochemical staining, were present and persisted in the GC light zone of LNs in abundant amounts not only before initiation of therapy but also during HAART, when no vRNA was detected in GCs. Consistent with immunohistochemical findings, specific antibody responses to HIV-1p17, -p24, and -gp120/gp41, as evaluated by ELISA and virus neutralization, persisted in patients under therapy for up to 13 months of follow-up. The implications of these findings are discussed in relation to HIV-1 persistence in infected individuals and the potential role of chronic antigenic stimulation by the deposited structural proteins in GCs for AIDS-associated B cell malignancies.

Fig. 1.

Changes in HIV RNA burden in the LNs during HAART. In situ hybridization for vRNA (green) before HAART (A) shows diffuse hybridization signals in the GC, representing FDC-bound vRNA and many virus-producing cells (arrow). The former is under limit of detection in the follow-up biopsy (B). Cells with HIV-1 gene expression are rare (arrow).

Fig. 2.

Persistence of HIV-1 structural proteins in the GC of patients under HAART. Frozen sections were immunolabeled for the capsid p24 (A and B), the matrix p17 (C and D), and the envelope glycoprotein gp120 (E and F). The amounts of HIV-1p24 and -p17 deposited in the GCs show no differences at baseline (A and C) and in the follow-up biopsy (B and D). The HIV-1gp120 was also detected in the follow-up biopsy (E) but not in GCs of tonsils obtained from an HIV-1 antibody-negative patient (F).

Fig. 3.

Detection-specific anti-HIV-1 antibodies directed against the matrix protein p17 (A), the capsid protein p24 (B), and the envelope glycoproteins (gp160) (C). Note the persistence of the HIV-1 antibody titers evaluated by ELISA. There was an ≈2- to 4-fold decrease in antibody titers against these HIV-1 structural proteins and glycoproteins under HAART.

Fig. 4.

Detection of virus neutralization antibodies against the R5 (A) and the X4 (B) HIV-1 isolates. Also the virus neutralizing antibodies persisted during the long-term HAART.