[Experimental studies of polymorphonuclear leukocyte on mandibular bone infection model in rabbit]

Polymorphonuclear leukocytes (PMN) play important roles in the prevention of infection at an early stage. We studied the function of these leukocytes using rabbit models of mandibular bone infection to evaluate the conditions which could not be reproduced in human beings Streptococcus milleri NCTC7331 and Bacteroides fragillis NCTC9343 were inoculated into the mandibular bone of rabbits using the Satoh-Heimdahl method, to produce supposed multiple infection models. Rabbits inoculated with these bacteria were used as a test group, and animals with surgically induced inflammation were used as a control group. We compared the number of leukocytes, the function of PMN, and histopathologic findings. 1) The number of leukocytes increased after treatment, reached a perk on day 3, gradually diminished later, but remained slightly higher than the baseline level on day 7, with persistence of inflammation in both groups. 2) Adhesiveness, ability to migrate and NBT reduction, were accelerated in both groups. 3) These functions of PMN accelerated more in the test group because the bacteria inoculated induced stronger inflammatory reactions and activated a series of infection defense mechanisms in the hosts. 4) Histopathologic examination after treatment showed invasion of inflammatory cells, predominantly leukocytes, in both groups, but heavier and more extensive infiltration in the group treated with the bacteria. All measurements were higher in the test group than the control group. These results showed that in the test group, causative or accompanied microorganisms activated the host's infection defense mechanisms and accelerated the functioning of PMN at an acute stage of infection.