Role of CD8+ and CD4+ T lymphocytes in jejunal mucosal injury during murine giardiasis

Abstract

T-cell-mediated pathogenesis has been documented in various idiopathic and microbially induced intestinal disorders. Diffuse microvillous shortening seen in giardiasis is responsible for disaccharidase insufficiencies and malabsorption of electrolytes, nutrients, and water. Other mucosal changes include crypt hyperplasia and increased numbers of intraepithelial lymphocytes (IEL). A recent report using an athymic mouse model of infection showed that these epithelial injuries were dependent on T cells. The aim of the present study was to identify which subset of superior mesenteric lymph node (SMLN) T cells were responsible for mucosal alterations in giardiasis. CD4+ and CD8+ T cells, as well as whole lymphocyte populations, were isolated from SMLN of Giardia muris-infected mice for adoptive transfer. Jejunal segments of recipient mice were assessed for brush border ultrastructure, sucrase activity, crypt/villus ratio, and IEL numbers. Mice that received enriched CD8+ and whole SMLN lymphocytes, but not CD4+ T cells, from infected donors showed diffuse shortening of microvilli, loss of brush border surface area, impaired sucrase activity, and increased crypt/villus ratios compared to respective controls. Transfer of whole SMLN lymphocytes, as well as enriched CD4+ or CD8+ T cells, from infected donors led to increased IEL numbers in the recipient jejunum. The findings indicate that loss of intestinal brush border surface area, reduced disaccharidase activities, and increased crypt/villus ratios in giardiasis are mediated by CD8+ T cells, whereas both CD8+ and CD4+ SMLN T cells regulate the influx of IEL.

FIG. 1.

Representative transmission electron micrographs of the jejunal microvillous brush border from naive mice which received lymphocytes from donors infected with Giardia (B, D, and F) or from sham-inoculated CDs (A, C, and E). In separate experiments, mice received either whole SMLN lymphocytes (A and B), enriched SMLN CD4⁺ T cells (C and D), or enriched SMLN CD8⁺ T cells (E and F). Brush border shortening, when present, was diffuse and was seen at sites of trophozoite colonization as well as in other areas. Bar equals 1 μm for all micrographs.

FIG. 2.

Jejunal sucrase activity in naive mice that received T-lymphocytes from donors. Donor mice were infected with G. muris (ID) or inoculated with medium alone (CD; solid line). Values (units per gram of protein) are expressed as a percentage of sucrase activity (mean ± SEM [error bars]) versus paired control (set at 100%, solid line). *, P < 0.05 versus paired CD (n = 8 to 12 mice per group).

FIG. 3.

Crypt/villus ratios in donor mice (donors) or in naive mice that received T-lymphocytes from donors 3 days posttransfer (whole lymphocyte preparation, CD4, CD8). Empty bars represent results from CDs or from naive recipients that received lymphocytes from CDs; solid bars represent results from IDs or from naive recipients that received lymphocytes from ID. Values are expressed as crypt/villus ratio (mean ± SEM [error bars]) per group. *, P < 0.05 versus paired CD group (n = 5 to 10 mice per group).

FIG. 4.

Jejunal IEL counts in mice that received lymphocytes from previously infected donors or from sham-inoculated CDs. Lymphocytes used were whole SMLN lymphocyte preparation, enriched CD4⁺ T cells, or enriched CD8⁺ T cells, and counts were performed 3 days after transfer. Values are expressed as number of IEL per 100 enterocytes (% IEL) (mean ± SEM [error bars]). (* P < 0.05 versus paired CD group; n = 5 to 10 mice per group).