Nasal associated lymphoid tissue & M cells, a window to persistent streptococcal infections

Background & objectives: Intranasal infection of mice has been used as a model of streptococcal pharyngitis, as nasal associated lymphoid tissue (NALT) in this animal is structurally and functionally analogous to human tonsils. The present study was carried out to determine whether group A streptococci preferentially colonized or invaded NALT. Methods: Lux⁺ strain Sp3 was created and exponential phase bacteria were introduced intranasally into BALB/C female mice, total photon emission from selected areas was quantified, sections of NALT tissues were used for immunofluorescent staining and M cell staining. Results: Intranasal infection of mice with bioluminescent group A streptococci or unlabeled streptococci demonstrated that NALT was a primary target of this pathogen. Streptococci readily gained access to the blood stream from this site of infection. Immunofluorescence microscopy studies showed that M cells, dispersed along the mucosal epithelium adjacent to NALT, were preferentially infected and likely to provide the window through which streptococci reached the underlying tissue. Interpretation & conclusion: The present study suggests that this upper respiratory Gram positive pathogen uses a mechanism similar to that of enteric pathogens in the intestine to gain access to underlying tissue, lymphatics and blood.