Changes in murine jejunal morphology evoked by the bacterial superantigen Staphylococcus aureus enterotoxin B are mediated by CD4+ T cells

Abstract

Bacterial superantigens (SAgs) are potent T-cell stimuli that have been implicated in the pathophysiology of autoimmune and inflammatory disease. We used Staphylococcus aureus enterotoxin B (SEB) as a model SAg to assess the effects of SAg exposure on gut form and cellularity. BALB/c, SCID (lacking T cells) and T-cell-reconstituted SCID mice were treated with SEB (5 or 100 microg intraperitoneally), and segments of the mid-jejunum were removed 4, 12, or 48 h later and processed for histochemical or immunocytochemical analysis of gut morphology and major histocompatibility complex class II (MHC II) expression and the enumeration of CD3+ T cells and goblet cells. Control mice received saline only. SEB treatment of BALB/c mice caused a time- and dose-dependent enteropathy that was characterized by reduced villus height, increased crypt depth, and a significant increase in MHC II expression. An increase in the number of CD3+ T cells was observed 48 h after exposure to 100 microg of SEB. Enteric structural alterations were not apparent in SEB-treated SCID mice compared to saline-treated SCID mice. In contrast, SEB challenge of SCID mice reconstituted with a mixed lymphocyte population or purified murine CD4+ T cells resulted in enteric histopathological changes reminiscent of those observed in SEB-treated BALB/c mice. These findings implicate CD4+ T cells in this SEB-induced enteropathy. Our results show that SAg immune activation causes significant changes in jejunal villus-crypt architecture and cellularity that are likely to impact on normal physiological processes. We speculate that the elevated MHC II expression and increased number of T cells could allow for enhanced immune responsiveness to other SAgs or environmental antigens.

FIG. 1

Photomicrographs of jejunal morphology in a control BALB/c mouse (a) and in experimental mice 4 (b), 12 (c), and 48 (d) h after challenge with 5 μg of SEB. After SEB treatment, villi are stunted and swollen, with evidence of edema, hypertrophy, and epithelial vacuolation (panel b, arrowheads). Also note crypt elongation 4 and 12 h after SEB treatment. Magnification, ×1,200 (a to c) or ×1,500 (d).

FIG. 2

Bar charts showing changes in villus height (a), crypt depth (b), and the villus:crypt ratio (c) in the jejuna of BALB/c mice treated with SEB (n = 10). ∗, P < 0.05 compared to control mice.

FIG. 3

Photomicrographs showing immunostaining of CD3⁺ T cells in the jejuna of a control BALB/c mouse (a) and mice treated with 5 μg of SEB 4 (b) and 48 (c) h previously. Note in panel b the altered villus-crypt morphology and the concentration of cells at the villus tip (some CD3⁺ cells are denoted by arrowheads and the asterisks indicate clusters of four or more CD3⁺ T cells). Magnification, ×160.

FIG. 4

Photomicrographs showing immunostaining of CD3⁺ T cells in the jejunum of a T-cell-reconstituted SCID mouse (a) and of a normal SCID mouse (b) 4 h after SEB challenge. T cells are readily apparent (arrowheads) in the lamina propria and mucosa of the reconstituted SCID mouse but were not identified, even at a higher magnification, in the jejuna from normal SCID mice. Magnification, ×200 (a) or ×250 (b).

FIG. 5

Photomicrographs of jejunal segments from a control SCID mouse (a) a SCID mouse treated 4 h previously with 5 μg of SEB (b), and a CD4⁺-reconstituted SCID mouse 4 h after SEB treatment (c). Jejunal segments from control and SEB-treated mice were virtually indistinguishable, whereas T-cell-reconstituted mice responded to SEB with a decrease in villus height and increased crypt depth. Magnification, ×100.