Nef functions in BLT mice to enhance HIV-1 replication and deplete CD4+CD8+ thymocytes.
BACKGROUND
The outcome of untreated HIV-1 infection is progression to AIDS and death in nearly all cases. Some important exceptions are the small number of patients infected with HIV-1 deleted for the accessory gene, nef. With these infections, disease progression is entirely suppressed or greatly delayed. Whether Nef is critical for high levels of replication or is directly cytotoxic remains controversial. The major problem in determining the role of Nef in HIV/AIDS has been the lack of tractable in vivo models where Nef's complex pathogenic phenotype can be recapitulated.


RESULTS
Intravenous inoculation (3000 to 600,000 TCIU) of BLT humanized mice with HIV-1LAI reproducibly establishes a systemic infection. HIV-1LAI (LAI) replicates to high levels (peak viral load in blood 8,200,000 ± 1,800,000 copies of viral RNA/ml, range 3,600,000 to 20,400,000; n = 9) and exhaustively depletes CD4+ T cells in blood and tissues. CD4+CD8+ thymocytes were also efficiently depleted but CD4+CD8- thymocytes were partially resistant to cell killing by LAI. Infection with a nef-deleted LAI (LAINefdd) gave lower peak viral loads (1,220,000 ± 330,000, range 27,000 to 4,240,000; n = 17). For fourteen of seventeen LAINefdd-infected mice, there was little to no loss of either CD4+ T cells or thymocytes. Both LAI- and LAINefdd-infected mice had about 8% of total peripheral blood CD8+ T cells that were CD38+HLA-DR+ compared <1% for uninfected mice. Three exceptional LAINefdd-infected mice that lost CD4+ T cells received 600,000 TCIU. All three exhibited peak viral loads over 3,000,000 copies of LAINefdd RNA/ml. Over an extended time course, substantial systemic CD4+ T cell loss was observed for the three mice, but there was no loss of CD4+CD8+ or CD4+CD8- thymocytes.


CONCLUSIONS
We conclude Nef is necessary for elevated viral replication and as a result indirectly contributes to CD4+ T cell killing. Further, Nef was not necessary for the activation of peripheral blood CD8+ T cells following infection. However, CD4+CD8+ thymocyte killing was dependent on Nef even in cases of elevated LAINefdd replication and T cell loss. This depletion of thymic T cell precursors may be a significant factor in the elevated pathogenicity of CXCR4 trophic HIV-1.
Division of Infectious Diseases, University of North Carolina, Chapel Hill, NC 27599-7042, USA.
Wei
W
Zou
Paul W
PW
Denton
Richard L
RL
Watkins
John F
JF
Krisko
Tomonori
T
Nochi
John L
JL
Foster
J Victor
JV
Garcia
D000163:Acquired Immunodeficiency Syndrome / Q000821:virology; D000595:Amino Acid Sequence; D000818:Animals; D018952:Antigens, CD34 / Q000378:metabolism; D015704:CD4 Antigens / Q000378:metabolism*; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism / Q000821:virology; D016827:CD8 Antigens / Q000378:metabolism*; D018414:CD8-Positive T-Lymphocytes / Q000378:metabolism / Q000821:virology; D057809:HEK293 Cells; D015497:HIV-1 / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*; D006801:Humans; D008213:Lymphocyte Activation; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D008969:Molecular Sequence Data; D012367:RNA, Viral / Q000378:metabolism; D019718:Receptors, CXCR4 / Q000378:metabolism; D060168:Thymocytes / Q000378:metabolism / Q000821:virology*; D013997:Time Factors; D019562:Viral Load; D014779:Virus Replication; D054311:nef Gene Products, Human Immunodeficiency Virus / Q000235:genetics / Q000378:metabolism*
D018952:Antigens, CD34; D015704:CD4 Antigens; D016827:CD8 Antigens; C514936:CXCR4 protein, mouse; D012367:RNA, Viral; D019718:Receptors, CXCR4; D054311:nef Gene Products, Human Immunodeficiency Virus; C514837:nef protein, Human immunodeficiency virus 1