Normal human intestinal B lymphocytes. Increased activation compared with peripheral blood.

Abstract

The state of activation of normal human intestinal mononuclear cells obtained from transplant donors was studied. Compared with PBMC, freshly isclated intestinal mononuclear cells expressed significantly more cell surface activation antigens on both B and T lymphocytes. Intestinal mononuclear cells contained significant numbers of immunoglobulin secreting cells immediately after cell separation. This population included CD5-positive B cells that secreted predominantly IgA. Cells from the large bowel consistently revealed higher numbers of IgA secreting cells than cells from the small bowel. Thus, intestinal B cells are markedly activated in vivo compared with PBMC and this increased activation correlates with increased spontaneous antibody secretion. B cells from the large intestine are more highly activated and secrete more antibody than do cells from the small intestine. The intestinal lamina propria lymphoid compartment exhibits a heightened state of activation that may be important for its distinct role in mucosal defense.

Mucosal Plasma Cell Repertoire During HIV-1 Infection

“…In this context, the preferential usage of V H 4 genes by B-1 B cells (88) could then account for both the decreased V H 3 expression and the increased V H 4 expression that we measured in lamina propria IgM-producing plasma cells. However, as noted above, convincing evidence supporting a prominent role for B-1 B cells in the human intestinal mucosa is quite limited to date (78,79).…”

“…The authors hypothesized that these were B1 B cells that develop outside of GCs and may preferentially target commensal bacteria in the intestine (77). However, the role of B-1 (CD5 ϩ ) B cells in the lamina propria of humans is controversial (78,79).…”

A Preponderance of CCR5+CXCR4+Mononuclear Cells Enhances Gastrointestinal Mucosal Susceptibility to Human Immunodeficiency Virus Type 1 Infection

“…Therefore, secondary lymphoid organs are the main sites of HIV replication in vivo (8,29). The majority of gastrointestinal mucosal T lymphocytes are memory cells and exhibit phenotypic and functional features of activation (31,34). This likely reflects the vital immunologic role these cells play at the major boundary between humans and the external environment.…”

Stimulated human lamina propria T cells manifest enhanced Fas-mediated apoptosis.

“…Despite the fact that lamina propria (LP) 1 T cells are in close proximity to potentially stimulatory mucosal antigens, and exhibit increased expression of surface markers of cell activation (1,2), the lamina propria is a site of controlled chronic inflammation normally (3,4). One immunologic mechanism that may at least partially explain this state of affairs involves the possibility that LP T cells are subject to immunologically induced programmed cell death (apoptosis) and are thus eliminated before they can mediate a deleterious immune response.…”