R5 strains of human immunodeficiency virus type 1 from rapid progressors lacking X4 strains do not possess X4-type pathogenicity in human thymus

Abstract

Some individuals infected with only R5 strains of human immunodeficiency virus type 1 progress to AIDS as quickly as individuals harboring X4 strains. We determined that three R5 viruses were much less pathogenic than an X4 virus in SCID-hu Thy/Liv mice, suggesting that R5 virus-mediated rapid disease progression is associated with host, not viral, factors.

FIG. 1

Virus ACH424 utilizes CCR5 but not CXCR4 in vitro. HOS cell lines expressing CD4, HIV-1 Tat-inducible green fluorescent protein (GFP), and either CXCR4 or CCR5 were infected with 1,000 50% tissue culture infective doses of ACH424, the R5 control virus Ba-L, or the X4 control virus NL4-3. After 6 days, the indicator cells were analyzed by flow cytometry for GFP expression. The percentage of GFP⁺ indicator cells (within the gate) is indicated inside each plot. The low-level infection of the HOS-CCR5 cell line by NL4-3 was likely mediated by low levels of endogenous CXCR4, known to be expressed on HOS cells.

FIG. 2

The three R5-AIDS viruses replicated to levels similar to those of Ba-L and not NL4-3. Thy/Liv cells were isolated from cohort 1 implants 17 days postinoculation and analyzed for intracellular p24 levels by quantitative ELISA. Each bar represents an individual implant.

FIG. 3

The three R5-AIDS viruses infected cell types similar to those infected by Ba-L and not NL4-3. Infected Thy/Liv implants were analyzed in situ 17 days postinoculation for HIV-1 p24 protein by immunohistochemistry. p24 protein is indicated in red, while cell nuclei are indicated in blue-purple. (A to F) Images of cohort 1 implants infected with Ba-L (A), NL4-3 (B), ACH172 (C), p198 (D and E), or ACH424 (F) for 17 days, revealing HIV-1 infection of cortical thymocytes (NL4-3) or medullary stromal cells (Ba-L and the R5-AIDS viruses). (G and H) Images of cohort 2 implants infected with p198 (G) or ACH424 (H) for 35 days, revealing HIV-1 infection of single cortical thymocytes. Magnifications, ×10 (A to D and F) and ×40 (E, G, and H).

FIG. 4

The three R5-AIDS viruses did not cause thymocyte depletion soon after inoculation. Thy/Liv cells isolated from representative implants 17 days postinoculation were analyzed by flow cytometry for surface expression of CD4 and CD8. The percentage of thymocytes expressing CD4 and CD8 is indicated in each plot. Uninfected Thy/Liv implants typically contain 80 to 90% CD4⁺ CD8⁺ thymocytes.