RESPONSE OF THE REGIONAL LYMPH-NODE TO BLUETONGUE VIRUS-INFECTION IN CALVES

Bluetongue virus (BTV) infection of cattle is characterized by prolong ed cell-associated viremia. In an effort to further evaluate the antiv iral response of BTV-infected cattle, the role of the regional lymph n ode (LN) in the immune response of calves to BTV was characterized. Ca lves were inoculated with BTV in the skin of the neck in an area drain ed by the superficial cervical LN. Calves were euthanized at regular i ntervals after inoculation and both BTV-challenged and contralateral ( control) superficial cervical LNs were harvested, In addition, some ca lves had cannulation of the superficial cervical efferent lymphatics p rior to inoculation. Lymphocyte subpopulation analysis was done on LN cell suspensions and lymph cells using a panel of cell-specific monocl onal antibodies. There was a significant increase in the proportion of B cells in the challenged LN after inoculation as compared with the c ontrol LN. In addition, BTV-specific antibodies were detected in effer ent lymph plasma from the challenged LN in one cannulated calf by 9 da ys after inoculation (DAI), as determined by competitive enzyme-linked immunosorbent assay, whereas BTV-specific antibodies were not detecte d in serum from this calf through 12 DAI. Analysis of lymph cells reve aled a sustained increase in cell output from the challenged LN due to an increase in lymphoblasts and CD8(+) T cells, In contrast, the cell output from the control LN dropped markedly by 8 DAI and there was no significant increase in any specific cell population. Double label an alysis characterized lymphoblasts as activated CD8(+) cells, as determ ined by expression of MHC Class II antigens (CD8(+) MHC II+). These ce lls were only transiently present as CD8(+) MHC II+ cells were not ide ntified in lymph from the challenged LN at 14 DAI. Few CD8(+) MHC IIcells were identified at any time in lymph from the control LN or in l ymph from a mock infected calf. The data indicate that B cell prolifer ation in the challenged LN and release of activated CD8(+) cells from this LN were specific responses to BTV infection. The rapid expansion of activated CD8(+) T cells indicates that these cells may limit early viral spread. It is concluded that the regional LN draining inoculate d skin is critical to the immune response of calves to BTV infection.