Morphologic and immunohistological characterization of the thymus of the X-linked severe combined immunodeficient dog

Paul William Snyder, Purdue University

Abstract

Severe combined immunodeficiency encompasses a heterogeneous group of diseases that are characterized by absent or severely impaired humoral and cellular immune responses. The mode of inheritance may be autosomal recessive, x-linked or sporadic. The pathological hallmark of these diseases is thymic dysplasia and lymphoid hypoplasia. The studies reported in this thesis were undertaken to characterize the morphologic and immunohistological changes in the thymuses of X-linked severe combined immunodeficient (XSCID) dogs. Additional studies were performed to develop reagents (monoclonal antibodies) that were employed to evaluate by immunohistological methods the dysplasia and lymphoid hypoplasia. In XSCID dogs the thymuses were reduced in size and often were obscured by adipose connective tissue. Microscopically, all thymuses were characterized by small lobules and fewer lymphocytes as compared to the age matched control dogs. Based on the presence of Hassall's corpuscles and branchial duct remnants, the degree of corticomedullary demarcation and lymphoid development and organization, three patterns of dysplasia and lymphoid hypoplasia were identified. Ultrastructurally, XSCID thymuses were characterized by a monomorphic population of epithelial cells and lacked the heterogeneous populations as has been previously noted in normal dogs. Monoclonal antibodies against canine thymic lymphocytes and epithelial cells were developed to immunohistologically characterize the thymic dysplasia and lymphoid hypoplasia in the XSCID dog. Eight anti-canine lymphocyte and six anti-canine thymic epithelial cell monoclonal antibodies were produced and characterized. These monoclonal antibodies permitted the delineation of lymphoid and epithelial cell populations within the normal canine thymus. Thymic dysplasia and lymphoid hypoplasia of canine XSCID were evaluated in situ by immunohistological methods using cryostat sections and monoclonal antibodies as markers of thymic cellular components. The more fully developed patterned XSCID thymuses were typified by greater numbers of lymphocytes that stained with a greater number of markers normally present in stages of T lymphocyte development. The XSCID thymuses which were of most underdeveloped pattern had fewer lymphocytes that were stained by the markers that identify mature T lymphocytes. The results of the anti-epithelial monoclonal antibody staining paralleled the lymphocyte staining with the XSCID thymuses with the greater number of lymphocytes stained by mature lymphocyte markers having the most developed and organized medullary epithelium. Again, the poorly developed XSCID thymuses had markedly reduced numbers of medullary epithelial cells that were poorly organized. The overall interpretation of these studies was that the canine thymus has microenvironments that can be detected using lymphoid and epithelial cell markers and that there are specific in situ abnormalities related to the lymphoid and epithelial development and organization in canine XSCD. These studies identified morphologic and immunohistologic abnormalities, but were unable to determine if the abnormalities were the direct result of the canine XSCID gene defect on the lymphocyte or epithelial cell or a combination of the two.

Degree

Ph.D.

Advisors

Felsburg, Purdue University.

Subject Area

Veterinary services

COinS