Numbers of granulocytes in thymic imprints of rabbits of different ages and degrees of coccidial parasitism

Abstract

Counts of granulocytes were performed on thymic imprints from normal rabbits 3 days old, 2–3 weeks old, and young adults, and from young adult rabbits mildly and severely parasitized with coccidiosis. Analyses of percentages of eosinophils, heterophils, and basophils indicated no sex differences. Comparisons of relative numbers of granulocytes in normal rabbits showed that young adult rabbits possessed more eosinophils and fewer basophils than the younger groups (no differences in heterophils); 3-day-old rabbits had more eosinophils than the 2-to 3-week animals (no differences in heterophils and basophils). No differences in relative numbers of the various granulocytes were found in the mildly and severely parasitized rabbits, but there was a decrease in eosinophils in the parasitized rabbits when compared with the young normal adult rabbits. Eosinophilic leukocytes were divided into two groups: the mononuclear "tissue" line and the lobated "blood" line of development. In the 3-day-old rabbits about 95% of eosinophils were of the lobed variety but in the older normal rabbits, the two developmental lines were about equal in numbers. When compared with the normal young adult rabbits, parasitized rabbits have increased percentages of "blood" eosinophils as a result of greater numbers of band and polymorphonuclear cells.

Hemopoiesis in the Thymus

“…Granulopoiesis is the thymus has been extensively documented since the late 1800s (see Bhatal and Campbell, 1965). More recently, granulocyte development has been shown in rodents (Sin and Sainte-Marie 1965;von Haelst, 1967;Kendall and Blackett, 1983;Kendall et al, 1985;Boshnakova, 1990) humans (Downey, 1948;Bhatal and Campbell, 1965), cats (Pack and Chapman, 1980), and rabbits (Downey, 1948;Westermann and Engelbert, 1969a, 1969b, 1969c. The embryonic and fetal stages of many animals show development of granulocytes within the thymus, and this activity may continue into adult life.…”

“…In many avian thymuses, mature eosinophils were found within vacuoles in or close to the necrotic center of Hassall's corpuscles (Kendall and Frazier, 1979). Associations of this nature were also observed in children (Bhatal and Campbell, 1965;Muller, 1977) and in rabbits (Westermann and Engelbert, 1969b). It has been suggested that they may be phagocytosing antigen-antibody complexes at this site because both antigen (Marshall and White, 1961) and immunoglobulins (Henry and Anderson, 1990) Several important questions arise from this activity.…”