The effect of aging on macrophage phenotype

Open Access
Moyer, Eric David
Area of Honors:
Letters, Arts, and Sciences (Abington)
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Dr. Steven Bloomer, Thesis Supervisor
  • Dr. David Ruth, Honors Advisor
  • Macrophage
  • Inflammation
  • iNOS
  • CD206
  • HO-1
  • Aging
  • Liver
  • Spleen
  • Immunofluorescence
  • Colorimetric
  • Immunohistochemistry
The increased inflammation accompanying aging has been partially attributed to a shift in macrophage phenotype. Macrophages, cells of innate immunity, exist within a spectrum ranging from proinflammatory (M1) to anti-inflammatory (M2). In this study, our goal was to compare the number of macrophages in spleens and livers of young and old rats. Some preliminary experiments were conducted on kidney tissue as well, though an analysis of splenic and hepatic tissue macrophages was the primary focus of this thesis research. Because of the increase in inflammation in old animals, I hypothesized that a greater number of macrophages would be observed in tissue samples from older animals compared to those from young, and that in old rats, the number of M1 macrophages would be elevated compared to M2 macrophages. I utilized immunohistochemical techniques to detect inducible nitric oxide synthase (iNOS; an M1 marker) and CD206, an M2 marker. In spleens, there was a trend towards increased iNOS+ macrophages in old animals, although this did not reach statistical significance. The number of splenic CD206+ macrophages was similar in samples from young and old rats. Old rat livers showed an increase in iNOS+ macrophages compared to young. Like the spleen, the number of hepatic CD206+ macrophages was similar between age groups. My data suggest that the overall increase in hepatic macrophages, especially of the M1 phenotype, may contribute to the increased inflammation with aging. Further studies are necessary to determine mechanisms causing an increase in liver macrophages, as well as in other organ systems.