The pathogenesis of L. monocytogenes strain Scott A was studied by challenging day-old male turkey poults by air sac inoculation with tryptose phosphate broth containing 10(0) cfu (control), 10(4), 10(5), and 10(6) cfu (low challenge), or 10(7) and 10(8) cfu (high challenge) of the Scott A (serotype 4b) strain of L. monocytogenes. Mortality at 2 wk postinfection (PI) ranged from 25% for low cha...

Mature T cells are derived from prethymic stem cells, which arise at one or more extrathymic sites and enter and differentiate in the thymus. The nature of these prethymic stem cells is a critical factor for the formation of the T-cell repertoire. Although the bone marrow of adult mice can provide such stem cells, their origin during murine embryogenesis is still undetermined. Among potential s...

Coxiella burnetii, phase I and II, cells cultivated in the yolk sac of chicken embryos were separated from host cell components by two cycles of isopycnic Renografin gradient centrifugation. Initial steps in the purification of viable C. burnetii involved differential centrifugation and sedimentation through an aqueous solution of 30% sucrose and 7.6% Renografin. After the first, but not the se...

AIMS The present study aimed to determine whether yolk sacs with abnormal sonographic appearance are associated with adverse perinatal outcomes in both early and late gestation. MATERIAL AND METHODS A total of 305 viable singleton pregnancies with gestational age of 6 to 9 weeks were prospectively evaluated with respect to perinatal outcomes and sonographic characteristics of the yolk sacs. ...

Cysteamine has been reported to modulate energy homeostasis and exert significant growth-promoting effects in broiler chickens. However, little is known concerning its effects on egg production of hens and the growth rate of their offspring. In the present study, 67-wk-old broiler breeders were allotted at random to control and cysteamine-supplemented (400 mg/kg) groups for 8 wk. The hatchlings...

Lymphocyte development and ontogenetic changes in erythroid cells have been studied in chick-chick yolk-sac-embryo chimeras differing at the B locus antigens. Erythroid cells derived from the yolk sac or from the intraembryonic mesenchyme were demonstrated by indirect immunofluorescence in the peripheral blood of these allogenic chimeras. At 7 days of incubation, yolk-sac-derived red cells repr...

The capacity of the yolk sac to generate multilineage, adult-type hematopoiesis was investigated in vivo using vascular endothelial-cadherin deficient embryos. In these mutants, the yolk sac is not connected to the vasculature of the embryo and therefore all hematopoietic activity detected therein is intrinsic to the yolk sac and not derived from intraembryonic sources. At embryonic days 9.5 an...

The potential absorptive role of the yolk sac membrane was evaluated by examining protein and enzyme patterns in embryonic fluids and by comparing the synthetic capacity of the secondary yolk sac, fetal liver and placenta for human chorionic gonadotrophin (HCG) and alpha-fetoprotein (alphaFP). In yolk sac fluid samples, protein electrophoresis showed two main electrophoretic bands with mobiliti...