Porphyromonas gingivalis virulence in a murine lesion model: Effects of immune alterations

This study utilized various mouse strains with documented alterations in immune system components to assess their contribution to modify the virulence of Porphyromonas gingivalis. P. gingivalis W50 was cultivated on blood agar plates, harvested and used to challenge mice by subcutaneous injection on the dorsolateral surface of the back. Soft tissue lesion development was estimated by measuring the area of the spreading lesion formed by this microorganism over a period of 15 days. Challenge of various normal inbred and outbred mouse strains including: BALB/cN, BALB/cJ, BALB/c nu/+, ICR, B1O.A(4R), B1O.MBR, A/J, C57BL/6J, CBA/CaH, C.B-17/ Icv TacfDF and C3H/HeN with 2 x 10¹⁰ bacteria showed similar lesion size among these strains (~ 400 mm²). Genetically deficient mouse strains [C.B-17/lcr Tac (SCID); DBA/2 (C5 deficient); BALB/ c nu/nu (T cell deficient); CBA/CaHN-XID/J (B cell deficient) and C3H/HeJ (LPS hyporesponsive)] demonstrated a lesion size which was similar to normal animals. C57BL/6J-BgJ (NK cell deficient) mice exhibited a significantly more severe lesion than the other strains tested. Following healing of the lesions, we initiated a secondary infection of the surviving animals to estimate the acquisition of protective immunity following recovery from the primary infection. Normal mice demonstrated a delayed onset and decrease in lesion size of 15 to 30% compared with the primary infection. In contrast, each of the immunodeficient strains appeared unable to develop immune protection to the secondary challenge. The findings suggest that protection against primary infections with P. gingivalis are mediated by innate immune mechanisms (PMN. NK cells). Additionally, it appears that T-cell-dependent humoral responses are critical to developing immunity to subsequent P. gingivalis infection.