Distribution of CD4⁺ and CD16⁺ cells in squamous epithelia of the oral and ectocervical mucosae and in simple columnar epithelia of the rectum/sigmoid and endocervix.

<p>Tissue sections were stained by standard IHC for CD4 (Panels <b>A,C,E,G</b>) or CD16 (Panels <b>B,D,F,H</b>), as described in Materials and Methods. Representative images are shown. Receptor-positive cells appear brown and cell nuclei appear blue. Arrows indicate a few examples of positive cells located within the epithelium. Small round CD4^bright cells (black arrows) are T cells, while antigen-presenting cells (APC) are larger and CD4^dim (yellow arrows). Note that CD4⁺ cells are typically present several cell layers deep within the stratified squamous epithelium and lamina propria of oral (<b>A</b>) and ectocervical mucosae (<b>C</b>), similar to CD16⁺ APC (<b>B</b> and <b>D</b>, respectively). Small round CD4^bright lymphocytes, CD4^dim APC and CD16⁺ APC are also present within the simple columnar epithelia (<b>E-H</b>). Note the horizontal orientation of CD16⁺ APC at the base of columnar cells in the endocervix (<b>F</b>). Also note that some CD16⁺ APC in the rectal epithelium are oriented vertically with dendritic processes reaching the luminal surface (insert, <b>H</b>). Bar = 100 μm.