Factors Involved in the Degeneration of Lymphoid Tissue in the Appendix

Abstract

Studies evaluating the age-related alteration of human appendix have been reported. Although the appendix shows a degeneration of lymphoid tissues with aging, the mechanism of action remains unclear. Surgically resected appendix tissues from patients with colon cancer, intestinal malrotation and ulcerative colitis (UC) were utilized for histological and flow cytometric analysis. Histological analysis showed that aging may induce steatotic changes in the appendix. However, there was no clear association between appendiceal fibrosis and aging. Lymphoid follicles in the appendix may start to develop before 5 days of age, gradually mature, and eventually disappear with aging. Flow cytometric analysis clearly identified a lymphocyte population in the appendix at 5 days, 45 and 75 years of age, and lymphoid follicles were also confirmed histologically. In contrast, lymphoid population was rarely detectable in the appendix at 79 and 80 years of age, and no lymphoid follicles were present histologically. Interestingly, cytograms from a case at 5 days of age suggested the existence of immature immune cells, as forward scatter showed an increase in cell size of the lymphocyte population. Histological analysis in UC patients found submucosal fat in the appendix of a case 66 years of age. Lymphoid follicular formation and mucosal structure were disrupted in cases of 70 and 72 years of age. UC patients may be more susceptible to steatotic change. Cytograms from appendices of UC patients also supported these histological findings. Our study confirms previous results that lymphoid tissues in the appendix degenerate over time, and proposes that inflammatory insult may facilitate the degenerative process in patients with UC.