Serum dioxin and immunologic response in veterans of Operation Ranch Hand

The authors studied immune response and exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin) among veterans of Operation Ranch Hand, the US Air Force unit responsible for the aerial spraying of herbicides in Vietnam from 1962 to 1971. A comparison group of Air Force veterans who served in Southeast Asia but were not involved in spraying herbicides was included. The authors studied delayed-type hypersensitivity skin test responses to Candida albicans, mumps, Trichophyton, and a bacterial antigen made from lysed Staphylococcus aureus. Lymphocyte measurements included total lymphocyte counts; T-cell (CD3, CD4, CD5, and CD8), B-cell (CD20), and NK-cell (CD16 and CD56) subsets; and expression of the activation antigen CD25 on CD3 T cells. The authors quantitated the serum concentrations of immunoglobulin (Ig)A, IgG, and IgM; examined sera for the presence of monoclonal immunoglobulins (M proteins); and looked for a broad range of autoantibodies (rheumatoid factor, antinuclear antibody, smooth muscle autoantibody, mitochondrial autoantibody, parietal cell autoantibody, and thyroid microsomal autoantibodies). They measured the level of dioxin in 1987 or 1992, extrapolated the result to the time of service in Vietnam, and assigned each veteran to one of four exposure categories: Comparison and three Ranch Hand groups (Background, Low, or High). Overall, the authors found no evidence of a consistent relation between dioxin exposure category and immune system alteration.