Studies indicate that lymphoid tissue (e.g., thymus, bone marrow, and Peyer's patches) shows evidence of increase apoptosis (A(o), a form of nonnecrotic cell death) during sepsis. However, it is not known if mucosal lymphoid tissue, such as lamina propria (LP), also shows evidence of increased A(o) and if so, is this associated with functional changes, i.e., cytokine gene expression in the LP. To examine this, male C3H/HeN mice were subjected to cecal ligation and puncture (CLP) and lamina propria mononuclear cells (LPMC) were harvested at 4 h (early sepsis) or 24 h (late sepsis). Alterations in the cell phenotype as well as A(o) (Tunel assay) were determined by three-color flow cytometry. Cytokine gene expression was assessed by multiprobe RNase protection assay. Sham LPMC preparations were found to be 34.4 ± 2.4% B220+ (B-cells), while 12.4 ± 2.1% were CD8+ (cytotoxic T-cells), 22.0 ± 0.8% were CD4+ (helper T-cells), and 6.4 ± 0.7% were F4/80+ (macrophages). The frequency of B220+ (9%*↑) and CD8 (6%*↑) populations increased markedly at 4 h after CLP; however, this increase was not seen at 24 h. The percentage of A(o)+ in CD8+, B220+, and F4/80+ cells increased markedly at both 4 and 24 h. CD4+ cells showed a marked increase in A(o) only at 24 h after CLP. When LPMC mRNA expression was examined, a significant increase in IL-2, -10, and -15 gene expression was observed only at 24 h but not 4 h after CLP. Thus, the early phenotypic changes associated with increased A(o) may be a reflection of localized immune cell activation in early sepsis contributing to the increased cytokine gene expression seen in late sepsis. This localized activation may contribute to gastrointestinal inflammation and/or immune dysfunction in sepsis.