title: The incidence of thymic B lymphoid follicles in healthy beagle dogs.
abstract: The incidence of thymic B cell lymphoid follicles was retrospectively studied in 62 male and 58 female healthy control beagle dogs (age 11.3 +/- 4.8, range 6 to 23 months). The animals were selected from toxicological studies performed in the period 1990-2001 at the Organon labs. The animals had received vehicle treatment. Thorough microscopic examination of the thymus in hematoxylin & eosin (H&E)-stained sections resulted in an unexpectedly high overall incidence of 70% of medullary lymphoid follicles. Occasionally, these lymphoid follicles contained germinal centers. With the use of a T- and B cell marker (respectively CD3 and CD79alpha) we confirmed that the lymphoid follicles exclusively contained large numbers of B lymphocytes. Moreover, with the use of the B cell marker, almost all animals (97%) prove to have B cell rich medullary areas. The study also confirmed that the dog thymus underwent progressive involution during the period from 6 to 23 months of age. As a consequence of the involution, B cell areas and lymphoid follicles may be obscured in some H&E sections. Results of this study indicated that dense B lymphocyte aggregates and/or B lymphoid follicles are a normal constituent of the canine thymus.
authors.affiliation: Department of Toxicology and Drug Disposition, NV Organon, Oss, The Netherlands. Jan-peter.ploemen@organon.com
authors.forename: Jan-Peter H T M
authors.initials: JP
authors.lastname: Ploemen
authors.forename: Wilma T M
authors.initials: WT
authors.lastname: Ravesloot
authors.forename: Eric
authors.initials: E
authors.lastname: van Esch
mesh_terms: D000818:Animals; D001284:Atrophy / Q000276:immunology / Q000473:pathology; D001402:B-Lymphocytes / Q000737:chemistry / Q000166:cytology / Q000276:immunology*; D015415:Biomarkers / Q000032:analysis; D004285:Dogs; D005260:Female; D018858:Germinal Center / Q000737:chemistry / Q000166:cytology / Q000276:immunology; D007150:Immunohistochemistry; D008297:Male; D009929:Organ Size; D013950:Thymus Gland / Q000737:chemistry / Q000166:cytology / Q000276:immunology*
chemical_list: D015415:Biomarkers