Effect of age and pregnancy on the antibody and cell-mediated immune responses of horses to equine herpesvirus 1.

The cell-mediated immune response and antibody response of horses of varying ages and of pregnant horses to equine herpesvirus 1 antigen were examined. Six to eight month old horses showed either no increase or slight increases in anti-equine herpesvirus 1 serum neutralizing antibody following vaccination and revaccination with a modified live equine herpesvirus 1 vaccine. However, these same horses showed a marked increase in the cell-mediated immune response to equine herpesvirus 1 as measured by the lymphocyte transformation test. Eighteen to 21 month old horses showed four to 64-fold increases in anti-equine herpesvirus 1 serum neutralizing antibody titer following vaccination, but the cell-mediated immune response to equine herpesvirus 1 was low or absent. Only after revaccination did they show an increased cell-mediated immune response to equine herpesvirus 1. The cell-mediated immune response of mares in the latter stages of pregnancy to equine herpesivurs 1 was suppressed although antibody titers increased as much as 16-fold following exposure to virulent equine herpesvirus 1.