The characteristics of 359 group A streptococcal (GAS) isolates collected from Chinese paediatric patients in two periods (1993–1994, 2005–2006) were studied. Isolates were assigned to emm types and assayed for eight superantigen (SAg) genes (speA, speC, speH, speI, speG, speJ, ssa, SMEZ). Types emm1 and emm12 were consistently the most prevalent during the two periods, while others varied in frequency. GAS isolates carrying six or more SAg genes increased from 46·53% (1993–1994) to 78·39% (2005–2006); ssa, speH and speJ genes (P<0·05) increased but speA declined (P<0·05). SAg gene profiles were closely associated with the emm type, but strains of the same emm type sometimes carried different SAg genes in the two periods. No significant difference in emm-type distribution and SAg gene profile was noted between isolates from different diseases. These data may contribute towards the development of a GAS vaccine in China.

Staphylococcal aureus epidermolytic toxins (ETs) A and B are responsible for the induction of staphylococcal scalded skin syndrome, a disease of neonates and young children. The clinical features of this syndrome vary from localized blisters to severe exfoliation affecting most of the body surface. Comparison of the crystal structures of two subtypes of ETs-rETA (at 2.0 Å resolution), rETB (at 2.8 Å resolution), and an active site variant of rETA, Ser195Ala at 2.0 Å resolution has demonstrated that their overall topology resembles that of a “trypsin-like” serine protease, but with significant differences at the N- and C-termini and loop regions. The details of the catalytic site in both ET structures are very similar to those in glutamate-specific serine proteases, suggesting a common catalytic mechanism. However, the “oxyanion hole,” which is part of the catalytic sites of glutamate specific serine proteases, is in the closed or inactive conformation for rETA, yet in the open or active conformation for rETB. The ETs contain a unique amphipathic helix at the N-terminus, and it appears to be involved in optimizing the conformation of the catalytic site residues. Determination of the structure of the rETA catalytic site variant, Ser195Ala, showed no significant perturbation at the active site, establishing that the loss of biological and esterolytic activity can be attributed solely to disruption of the catalytic serine residue. Finally, the crystal structure of ETs, together with biochemical data and mutagenesis studies, strongly confirms the classification of these molecules as “serine proteases” rather than “superantigens.”

The interaction between Heligmosomoides polygyrus superantigen and human peripheral blood mononuclear cells (PBMC) was evaluated. Parasite homogenate and excretory–secretory proteins from both L4 larvae and adult worms were examined for their ability to stimulate, and be presented by, human cells. Proliferation assays using PBMC from 3 human volunteers indicated that naïve cells were stimulated by H. polygyrus superantigen. Antigen presenting cells (APC) from a number of human donors were able to successfully present H. polygyrus superantigen to mouse T cell hybridomas. However, this ability varied according to the source of the superantigen, and human APC, in contrast to APC from mice, could only present the superantigen contained within parasite homogenate. Also, in contrast to the situation with mice, human APC could present H. polygyrus superantigen to stimulate mouse T cells expressing not only TCR Vβ8.1, but also TCR Vβ7. Therefore, H. polygyrus superantigen can successfully stimulate, and be presented by, human PBMC of different MHC haplotypes, although the cellular mechanisms appear to be different from those observed in the mouse.