Chapter 5 - Radiation-associated changes in the colon of rhesus macaques

Abstract

Colonic epithelial depletion was common in animals irradiated at 12Gy but was less common and less severe in animals irradiated at 11 or 10Gy. Depleted or newly regenerative mucosal epithelium had reduced goblet cell populations, which would reduce the protective mucin on the mucosal surface. Despite the mucosal epithelial injury, immunohistochemical (IHC) staining for lipopolysaccharide core antigen rarely indicated penetration of mucosal microbes into the submucosal tissues. Overt inflammatory cell infiltration was not a prominent feature of the radiation-associated colonic injury but IHC staining revealed an increased population of MxA+ (activated) leukocytes in the colonic mucosa, indicating a radiation-associated change in the activation status of preexisting leukocyte populations. The colon of irradiated animals had an increased population of macrophages, as revealed by myeloperoxidase IHC staining, but CD38 IHC staining did not reveal an increase in pro-inflammatory macrophages. By contrast, IHC staining for CD163 revealed an increase in the mucosal population of profibrotic macrophages.