Bragdon v. Abbott, 524 U.S. 624, 11 (1998)

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634

BRAGDON v. ABBOTT

Opinion of the Court

virus invades different cells in the blood and in body tissues. Certain white blood cells, known as helper T-lymphocytes or CD4[H11501] cells, are particularly vulnerable to HIV. The virus attaches to the CD4 receptor site of the target cell and fuses its membrane to the cell's membrane. HIV is a retrovirus, which means it uses an enzyme to convert its own genetic material into a form indistinguishable from the genetic material of the target cell. The virus' genetic material migrates to the cell's nucleus and becomes integrated with the cell's chromosomes. Once integrated, the virus can use the cell's own genetic machinery to replicate itself. Additional copies of the virus are released into the body and infect other cells in turn. Young, The Replication Cycle of HIV-1, in The AIDS Knowledge Base, pp. 3.1-2 to 3.1-7 (P. Cohen, M. Sande, & P. Volberding eds., 2d ed. 1994) (hereinafter AIDS Knowledge Base); Folks & Hart, The Life Cycle of Human Immunodeficiency Virus Type 1, in AIDS: Etiology, Diagnosis, Treatment and Prevention 29-39 (V. DeVita et al. eds., 4th ed. 1997) (hereinafter AIDS: Etiology); Greene, Molecular Insights into HIV-1 Infection, in The Medical Management of AIDS 18-24 (M. Sande & P. Volberding eds., 5th ed. 1997) (hereinafter Medical Management of AIDS). Although the body does produce antibodies to combat HIV infection, the antibodies are not effective in eliminating the virus. Pantaleo et al., Immunopathogenesis of Human Immunodeficiency Virus Infection, in AIDS: Etiology 79; Gardner, HIV Vaccine Development, in AIDS Knowledge Base 3.6-5; Haynes, Immune Responses to Human Immunodeficiency Virus Infection, in AIDS: Etiology 91.

The virus eventually kills the infected host cell. CD4[H11501] cells play a critical role in coordinating the body's immune response system, and the decline in their number causes corresponding deterioration of the body's ability to fight infections from many sources. Tracking the infected individual's CD4[H11501] cell count is one of the most accurate measures of the course of the disease. Greene, Medical Management of

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