CD4 T cells and major histocompatibility complex class II expression influence worm expulsion and increased intestinal muscle contraction during Trichinella spiralis infection

Abstract

Expulsion of intestinal nematode parasites and the associated increased contraction by intestinal muscle are T cell dependent, since both are attenuated in athymic rodents. The CD4 T-cell subset has been strongly associated with worm expulsion; however, the relationship between these cells, antigen presentation, and worm expulsion is not definitive and the role of these factors in intestinal muscle hypercontractility has not been defined. We infected C57BL/6, athymic, CD4-deficient, CD8alpha-deficient, and major histocompatibility complex class II (MHC II)-deficient (C2d) mice with Trichinella spiralis larvae. We examined intestinal worm numbers, longitudinal muscle contraction, and MHC II expression. Numerous MHC II-positive cells were identified within the muscularis externa of infected but not uninfected C57BL/6 mice. C57BL/6 and CD8alpha-deficient mice developed large increases in muscle contraction, expelling the parasite by day 21. Athymic and C2d mice exhibited much smaller increases in muscle contraction and delayed parasite expulsion. CD4-deficient mice exhibited intermediate levels of muscle contraction and delayed parasite expulsion. To further examine the role of MHC II and CD4 T cells, we irradiated C2d mice and reconstituted them with C57BL/6 bone marrow alone or with C57BL/6 CD4 T cells. C57BL/6 bone marrow alone did not affect muscle function or worm expulsion in recipient C2d mice. Partial CD4 T-cell reconstitution was sufficient to restore increased muscle contraction but not worm expulsion. Thus, hematopoietic MHC II expression alone is insufficient for the development of muscle hypercontractility and worm expulsion, but the addition of even small numbers of CD4 T cells was sufficient to induce intestinal muscle pathophysiology.

FIG. 1

Time course of the contractile response to 1 μM carbachol (the y axis shows the maximum tension generated) by intestinal muscle taken from infected C57BL/6 mice. Data shown are the mean ± 1 SEM of groups of four to six animals. The asterisk denotes a significant increase in tension compared to tissues from uninfected mice (time = 0 days).

FIG. 2

Maximum tension generated by muscle from uninfected mice (A) or day 8 p.i. mice (B) in response to 1 μM carbachol. Mouse strains shown are euthymic C57BL/6 (solid bar), athymic C57BL/6 (open bar), CD8α-deficient (hatched bar), CD4-deficient (cross-hatched bar), and C2d (finely cross-hatched bar). Data shown are the mean ± 1 SEM from groups of four to six animals. The asterisk denotes significantly lower tension generation by muscle compared to the infected C57BL/6 mice.

FIG. 3

Immunohistochemistry for detection of cells expressing MHC II and F4/80 within the small intestinal tissues of normal uninfected mice (A and B) or mice at 8 days p.i. (C to F). (A) Jejunal cross-section from an uninfected euthymic C57BL/6 mouse. Dark red staining is localized to cells within a lymphoid follicle (arrow, bottom right) as well as more diffuse staining of some epithelial cells (upper arrow). Magnification, ×40. (B) Jejunal cross-section from an uninfected C2d mouse, revealing absence of staining, even in a lymphoid follicle. Magnification, ×40. (C) Numerous stained cells localized to the external muscle layers of jejunal tissue (arrows) from a euthymic C57BL/6 mouse 8 days p.i. Magnification, ×400. (D) Serial section from panel C, with staining for F4/80 (for mature macrophages), showing that F4/80 staining colocalizes with many of the MHC II-positive cells found in the external muscle layers (arrows) of euthymic mice on day 8 p.i. Magnification, ×400. (E) Absence of MHC II staining in the external muscle layers and crypts of a C2d mouse on day 8. Magnification, ×400. (F) Many cells stain for MHC II within the muscle layers, myenteric plexus, and crypts of a C2d mouse (arrows), reconstituted with C57BL/6 bone marrow, on day 8 p.i. Magnification, ×400.

FIG. 4

Maximum tension generated, in response to 1 μM carbachol, by intestinal muscle from infected euthymic C57BL/6 mice (solid bar) and C2d mice without manipulation (open bar) or reconstituted with bone marrow from C57BL/6 mice (hatched bar) or with bone marrow plus CD4⁺ T cells (cross-hatched bar) 8 days p.i. Results shown are the mean ± 1 SEM of groups of four animals. The asterisk denotes a significantly lower tension generation by muscle compared to the infected C57BL/6 mice.