Staphylococcal enterotoxin H contrasts closely related enterotoxins in species reactivity

Abstract

Staphylococcus aureus enterotoxin H (SEH) belongs to the staphylococcal enterotoxin (SE) family of superantigens (SAgs). SEH has structural similarities to other SE; however, its biological properties are less well characterized. SEH binds with high affinity to human major histocompatibility complex (MHC) class II and exhibits strong mitogenic activity in human T cells, although it was found to be less potent than the related SEA. Surprisingly and in sharp contrast to related SEs, SEH did not possess superantigen activity in murine T cells and T cells from three investigated rat strains. However, SEH bound to a high extent to murine MHC class II expressing cells and when presented by these cells SEH stimulated human T cells to proliferate. Thus, SEH interacts with the murine MHC class II molecule in a functional manner. Notably, SEH had an inhibitory effect on murine SEA response, demonstrating that SEH interferes with the SEA interactions with murine cells. Despite this, murine T cells did not proliferate regardless of whether SEH was presented on human or murine MHC class II expressing cells. Consequently, SEH differs in species reactivity as compared to related SEs and lacks critical properties for T-cell activation in mice. We propose that unlike other SEs, SEH does not interact with murine T cells since it is not recognized by murine T-cell receptors.

Figure 1

Superantigen-induced proliferation of human PBMC. Proliferation was determined by [³H]thymidine incorporation following 72 hr of culture. Data from one of 16 individuals are shown. Error bars indicate standard deviations. For more details about the individual donors, see Table 1.

Figure 2

Proliferative response to superantigen stimulation in bulk spleen cell cultures from (a) outbred mice and (b) inbred mice. Proliferation was determined by [³H]thymidine incorporation following 72 hr of culture. Data from one of two representative experiments are shown and error bars indicate standard deviations.

Figure 3

Flow cytometric histograms showing surface bound superantigen on (a) live gated Raji cells (b) live gated A20 cells and (c) live and CD19⁺ gated spleen cells from C57BL/6 mice. Data from one of two representative experiments are shown.

Figure 4

The influence of SEH on SEA induced cytotoxic activity in murine T cells. C57BL/6 mice were treated i.v. with SEA 2 days prior to analysis of the cytotoxic activity of CD8⁺ spleen cells against SEA coated A20 target cells in the presence or absence of SEH. The effector : target cell ratio used was 10 : 1. Background levels of spontaneous lysis of target cells have been subtracted from the values. Data from one of three representative experiments are shown and error bars indicate standard deviations.

Figure 5

T-cell proliferation following superantigen stimulation in the presence of either human or murine irradiated MHC class II⁺ cells. (a) CD4⁺ human PBMC cultured with human lipopolysaccharide (LPS) activated syngeneic CD19⁺ PBMC. (b) CD4⁺ human PBMC cultured with LPS activated CD19⁺ spleen cells from C57BL/6 mice. (c) CD4⁺ spleen cells from C57BL/6 mice cultured with human LPS activated CD19⁺ PBMC. (d) CD4⁺ spleen cells from C57BL/6 mice cultured with LPS activated syngeneic CD19⁺ spleen cells. Proliferation was determined by [³H]thymidine incorporation following 72 hr of culture. Data from one of three representative experiments are shown and error bars indicate standard deviations.