Studies on the mechanism of vaccinal immunity to Marek''s disease

Current knowledge of the nature of the antigens and of the host immune responses in vaccinal immunity to Marek's disease is reviewed. It is suggested that a two-step mechanism of resistance operates. The first step involves humoral and cell-mediated responses directed against viral antigens; the second step occurs after challenge with Marek's disease virus and consists of cellmediated responses directed against tumour cells.     

Co-culture of ovine ova with oviductal cells in medium 199

Three experiments were conducted to test the suitability of medium 199 supplemented with 10% fetal calf serum (M199FCS) as a medium for co-culture of one-cell sheep ova with sheep oviductal cells. In Exp. 1, ova were co-cultured for 5 d in 5 ml of M199FCS or in Ham's F10 medium supplemented with 10% fetal calf serum (F10FCS). Co-culture did not increase the number of cleavages at the end of 5 d of culture, but M199FCS supported more cleavages than did F10FCS (P = .016). In Exp. 2, ova were cultured for 1 to 3 d in M199FCS alone or on oviductal, uterine or kidney cell monolayers from ewes 2 d postestrus and transferred to recipients from which they were recovered at 8 d postestrus. Co-culture with oviductal cells improved (P less than .001) the cleavage index of recovered embryos compared with culture in medium alone or co-culture with other cell types. In Exp. 3, monolayers of oviductal cells from ewes 2 d postestrus and from luteal-phase ewes were cultured as in Exp. 2. No difference was observed between the two sources of oviductal cells for their ability to support in vitro development of one-cell sheep eggs for 1 or 2 d. These studies suggest that M199FCS may be a good medium to use in an oviductal cell co-culture system for one-cell sheep ova. Results further suggest that specific secretions of oviductal cells may be important for early embryo development in vivo.     

Detection of Toxoplasma gondii in the milk of experimentally infected lactating cats.

Tachyzoites of Toxoplasma gondii have been found in the milk of sheep, goats, cows and mice and infection by ingestion of raw goat milk has been documented in humans. Lactational transmission from infected cats to their kittens is suspected but the organism has not been detected in the milk. The purpose of this study was to demonstrate the presence of T. gondii in the milk of experimentally infected cats. Pregnant specific pathogen free cats were inoculated orally with T. gondii at various times prior to parturition. Feces were examined for oocyst shedding after sugar solution centrifugation. Milk was collected for polymerase chain reaction (PCR) and bioassay in mice. T. gondii was detected in the milk of five of six cats by either bioassay or PCR.     

Effect of primary phase feline immunodeficiency virus infection on cats with chronic toxoplasmosis.

The effect of primary phase feline immunodeficiency virus (FIV) infection on clinical signs, hematological values, Toxoplasma gondii oocyst shedding, T. gondii-specific serology, T. gondii-specific cell-mediated immune responses, non-specific cell-mediated immune responses, and lymphocyte subpopulations from cats with experimentally induced chronic toxoplasmosis was studied. No significant clinical or hematologic abnormalities were noted following inoculation with FIV. T. gondii-specific IgM was significantly increased, concanavalin A, T. gondii tachyzoite antigen and T. gondii secretory antigen induction of lymphocyte transformation were significantly suppressed, and CD4+ cell numbers were significantly decreased following inoculation with FIV. The changes were attributed to FIV effects on the immune system and resultant activated toxoplasmosis.