A polarized Th1 type immune response to Cowdria ruminantium infection is detected in immune DBA/2 mice

Immune responses to Cowdria ruminantium, an intracellular organism that cau ses heartwater in domestic ruminants, were characterized in a DBA/2 mouse m odel. immunity induced by infection and treatment was adoptively transferab le by splenocytes and could be abrogated by in vivo depletion of T cells bu t not by inhibition of nitric oxide synthase using N-G-monomethyl-L-arginin e. IgG2(a) and IgG2(b) C. ruminantium-specific responses were detected in i mmune mice. Culture supernatants of splenocytes from immune DBA/2 mice, whi ch were stimulated with crude C. ruminantium antigens or recombinant major antigenic proteins 1 or 2, contained significant levels of interferon (IFN) -gamma and interleukin (IL)-6, but insignificant levels of IL-1 alpha, IL-2 , IL-4, IL-5, IL-10, IL-12, tumor necrosis factor-alpha (TNF), and nitric o xide. A similar response was detected during primary infection, although IF N-gamma levels decreased significantly during clinical illness and then inc reased following natural or antibiotic-aided recovery. These data support t he conclusion that protective immunity to C. ruminantium in DBA/2 mice is m ediated by T cells and is associated with a polarized T helper 1 type of im mune response. This murine model could be utilized to screen for protective C. ruminantium antigens that provoke Th1 type immune responses and for eva luation of these antigens in recombinant vaccines against heartwater.