Figure 1. SIV is present in the rectal epithelium as early as four hours post infection.

Serial paraffin sections of R-H4.1 (sacrificed four hours pi; A and B) and R-H16.2 (sacrificed sixteen hours pi; C and D) were labeled by IHF for gp130 (Alexa-546, A and C), CD3 (TRITC, B and D) or fascin (Alexa-488, B and D) and nuclei were stained with DAPI (A–D). CR, crypt; LP, lamina propria; RL, rectal lumen. Arrows on serial sections point to intraepithelial T lymphocytes positive for SIV antigens. Cell-associated virus in the epithelial cell fraction was assayed by co-culture of cells isolated from the rectum. Results are expressed as TCID₅₀ per million cells. The viral load does not increase over the first four days of infection; + the TCID₅₀ could not be calculated due to small number of wells positive for SIV antigen (E).