A sensitive peptide-major histocompatibility complex II (pMHCII) tetramer-based method was used to determine whether CD4+ memory T cells resemble the TH1 and TH-17 subsets described in vitro. Intravenous or intranasal Listeria monocytogenes infection induced pMHCII-specific CD4+ naïve T cells to proliferate and produce effector cells, about 10% of which resembled TH1 or TH-17 cells, respectively. TH1 cells were also present among the memory cells that survived three months post-infection whereas TH-17 cells disappeared. The short lifespan of TH-17 cells was associated with low amounts of Bcl-2, interleukin 15 receptor, CD27 and little homeostatic proliferation. These results suggest that TH1 cells induced by intravenous infection are more efficient at entering the memory pool than TH-17 cells induced by intranasal infection.

Although infection by group A streptococc is a model of extracellular mucosal pathogenesis, these organisms can be associated with highly invasive infections resulting in sepsis and shock. Over the last 6 yr this species has renewed its reputation as a si nt cause of sepsis and has piqued interest in the m nim by which some strains are better able to breach mucosal barriers to gain access to the bloodstream than are others. An ite tion assay was developed on the basis of resistance of intacellular streptococci to penicillin and gentamicin. Experiments showed that stationary-phase, as opposed to logarithmic-phase, bacteria are efficiently internalized and can persist in cultured human cells. Electron microscopy confirmed that streptococci were contained within intraceflular vacuoles. Various strains of streptococci revealed signicant differences in their capacity to be intenalied. Two type Ml streptococci Isolated from blood infections were internalized at frequencies equal to those reported for Sabnonella and Listeria monocytogenes and greater than the frequency of a cional variant from a case of pharyngitis.Numerous mucosal pathogens that readily invade the bloodstream have the capacity to be internalized and to persist within human epithelial cells (1). Although the importance of intracellular invasion in pathogenesis is debated by some, there is general agreement that this process can lead to invasion of deeper tissue and blood. The capacity ofListeria (2), Shigella (3), Salmonella (4), and several Yersinia species (5) to invade epithelial cells is entirely consistent with the pathophysiology associated with their infections. Listeria monocytogenes has become the paradigm for Gram-positive intracellular infections (6). L. monocytogenes possesses the adhesin internalin that mediates internalization and shares structural similarities to streptococcal surface proteins (6). In addition, both group A streptococci and L. monocytogenes express highly related thiol-activated hemolysins (7). Until recently, streptococcal species were traditionally considered to be extracellular pathogens of the oral or vaginal mucosa, even though some species have long been recognized to cause deadly blood or meningeal infections. Group A streptococci are commonly associated with pharyngitis and impetigo, but the recent resurgence of blood infections caused by this species has reminded the public health community of their potential to invade deeper tissues and the bloodstream and to cause significant morbidity (8,9 RPMI-1640 (1 ml) containing gentamicin (100 Ag/ml) and penicillin (5 pg/ml) was then added to wells to eliminate extracellular bacteria. Neither antibiotic penetrates eukaryotic cells (16). Infected monolayers were incubated at 370C for various time periods depending on the experiment before they were washed and dispersed by addition of 100 A4 of 0.25% trypsin/l mM EDTA. Streptococci were released from disrupted monolayers by the addition of 400 pA of 0.025% Triton X-100 (10). In later experiments, monolayers were...

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Human tonsils are suspected to be an antibiotic-impervious human reservoir for group A streptococcus. An intranasal infection model in mice and a bioluminescent-tagged strain were used to investigate this possibility. Viable streptococci were predominantly found both intra- and extracellularly in nasal-associated lymphoid tissue (NALT), a human tonsil homologue. Ulex europaeus-1, a membranous (M) cell-specific lectin, identified cells harboring streptococci at the epithelial surface of NALT and blocked bacterial colonization of this tissue. These results suggest that M cells in NALT transport this Gram-positive pathogen across the epithelial layers in a manner similar to those in Peyer’s patches, which permit enteric pathogens to invade deeper tissues from the gastrointestinal tract.

The group B streptococcus (GBS) is a major cause of pneumonia, sepsis, and meningitis in neonates and a serious cause of mortality or morbidity in immunocompromised adults. Although these streptococci adhere efficiently and invade a variety of tissue-specific epithelial and endothelial cells, adhesins and invasins are still unknown. All serotypes of GBS studied to date express C5a peptidase (SCPB) on their surface. This investigation addresses the possibility that this relatively large surface protein has additional activities. Rabbit anti-SCPB serum inhibited invasion of lung epithelial A549 cells by the serotype Ia strain O90R, suggesting that SCPB is an invasin. This was confirmed by inserting an in-frame 25-amino-acid deletion into the scpB gene. Invasion of HEp2 and A549 human cell lines was significantly reduced by the mutation. Enzyme-linked immunosorbent assays were used to demonstrate that purified SCPB protein binds directly to HEp2 and A549 cells and also binds the extracellular matrix protein fibronectin. Binding was dose dependent and saturable. These results suggested that SCPB is one of several potential invasins essential for GBS colonization of damaged epithelium.