Characterization of Gut-Associated Lymphoid Tissue (GALT) of Normal Rhesus Macaques

This study characterizes the gut-associated lymphoid tissue (GALT) of normal healthy rhesus macaques and compares the percentages of T and B cell subsets to those of systemic lymphoid tissue. Lymphocytes from the systemic lymphoid tissue (spleen, axillary, and inguinal lymph nodes), mesenteric lymph nodes (MLN), and intestinal epithelium (IEL) and lamina propria (LPL) of the jejunum, ileum, and colon were examined from both adult and juvenile, normal rhesus macaques. Lymphocytes were analyzed for expression of CD2, CD3, CD4, CD8, CD25, γδ TCR, and CD20 by two- or three-color flow cytometric analysis. Sections of jejunum, ileum, and colon were examined for CD3, CD20, and CD103 expression by immunohistochemistry. Peyer's patches were also examined for CD3, CD4, CD8, and CD20 expression by immunohistochemistry. Most IEL and LPL were CD103⁺, CD3⁺T cells with significantly fewer CD20⁺B cells. The IEL were predominantly CD3⁺CD8⁺(63–80%), with very few CD4⁺cells, whereas CD4:CD8 ratios in the LPL ranged from 0.74 to 1.3. Three to 38% of the IEL were γδ TCR positive, but γδ expression was rare in the LPL and MLN. γδ TCR expression was also higher in the IEL of younger animals. LPL had higher expression of CD25 compared to IEL and systemic tissues, particularly in aged animals. CD4⁺CD8⁺, double-positive and CD3⁺CD4⁻CD8⁻double-negative cells were also observed in GALT. These results demonstrate that GALT of rhesus macaques is remarkably similar to that of humans, further justifying the use of these animals as models for various intestinal disorders.