SummaryVery little is known about the biological functions of pili that have recently been found to be expressed by important Gram-positive pathogens such as Corynebacterium diphtheriae, Streptococcus agalacticae, S. pneumoniae and S. pyogenes. Using various ex vivo tissue and cellular models, here we show that pili mediate adhesion of serotype M1 S. pyogenes strain SF370 to both human tonsil epithelium and primary human keratinocytes, which represent the two main sites of infection by this human-specific pathogen. Mutants lacking minor pilus subunits retained the ability to express cell-surface pili, but these were functionally defective. In contrast to above, pili were not required for S. pyogenes adhesion to either immortalized HEp-2 or A549 cells, highlighting an important limitation of these extensively used adhesion/invasion models. Adhering bacteria were internalized very effectively by both HEp-2 and A549 cells, but not by tonsil epithelium or primary keratinocytes. While pili acted as the primary adhesin, the surface M1 protein clearly enhanced adhesion to tonsil, but surprisingly, had the opposite effect on adhesion to keratinocytes. These studies provide clear evidence that S. pyogenes pili display an adhesive specificity for clinically relevant human tissues and are likely to play a critical role in the initial stages of infection.

The tonsil epithelium synthesizes an array of antimicrobial cationic peptides which function as host defence. Preliminary immunohistochemical data suggest that the surface epithelium of tonsils from recurrent acute tonsillitis patients contains reduced amounts of such peptides, which may increase these patients' susceptibility to infection.

A histochemical investigation of age-related changes that occur with respect to the localization of NADPH-diaphorase in the ganglionated plexus of the guinea-pig gallbladder was carried out. In all age groups examined (embryonic stages day 34 and 52, 2 to 4-day old, 6-month old and 2-year old), the mean percentage of NADPH-diaphorase-positive neurons per ganglion was obtained by taking the number of neurons that were immunoreactive to protein gene product 9.5 (a general neuronal marker) as 100%. In addition, the possible co-existence of NADPH-diaphorase and nitric oxide synthase in the ganglionated plexus of 2 to 4-day old and 6-month old guinea-pig gallbladder was investigated. NADPH-diaphorase was not present in the ganglionated plexus of the gallbladder at embryonic day 34. At embryonic day 52, all the protein gene product 9.5-immunoreactive neurons showed positive staining to NADPH-diaphorase; this dropped to a minimum at 2-4 days (26.7%), rose slightly at 6 months (33.6%), and finally returned close to the 100% value at 2 years. In the gallbladders of 2-year old guinea-pigs, some (3 out of 10) ganglia were devoid of protein gene product 9.5-immunoreactive neurons, but NADPH-diaphorase-stained granules were found within the ganglia. However, all those neurons that were immunopositive to protein gene product 9.5 also expressed NADPH-diaphorase. Moreover, NADPH-diaphorase-positive neurons in the gallbladder of 2 to 4-day-old and 6-month-old guinea-pigs were found to express nitric oxide synthase.

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