Leprosy has been thought the disease of skin and peripheral nervous system because of its characterictic signs and symptoms. However, some patients show the signs of central nervous disturbances such as bulbar palsy, chorea and so on. To analyse the mechanisms of those peculiar diseases, the author investigated the distribution of ParaRosanilin Positive Materials (LPPM) and tissue injuries in the central nervous system histopathologically with the use of periodic acid-carbol pararosanilin stain (Harada method).

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In this superinfection experiment, male mice of BALB⁄c strain were used. It is very characteristic in susceptibility to M. lepraemurium, strains Hawaiian-M (HM) and Hawaiian-B (HB), that HM bacilli inoculation of male BALB⁄c mice produced benign type leproma, while HB bacilli inoculation produced large malignant leproma at the subcutaneous infection site.
These mice were subcutaneously inoculated with HM bacilli (2.8×10⁶) and⁄or with HB bacilli (5.0×10⁶) on their abdomen. Ten weeks after primary infection, these mice were superinfected subcutaneously with HM bacilli (1.0×10⁶) and⁄or with HB bacilli (5.0×10⁶) on their thorax, respectively. Age-matched male mice of BALB⁄c strain were used as controls for the superinfection.
Some delay was clearly observed in onset and development of leproma at the superinfection site, compared with those of control mice, in almost all the cases. Leproma develpment was weakly suppressed in the mice primarily infected with HB bacilli and superinfected with HB bacilli. In contrast, higher suppression was found in the mice primarily infected with HM bacilli and superinfected with HM bacilli. Particularly, it is of interest that HB bacilli inoculation of the mice primarily infected with HM bacilli produced benign type leproma, whereas HB bacilli inoculation of control mice produced large malignant leproma. Hereupon, in this due combination of primary infection with HM bacilli and superinfection with HB bacilli, conversion of disease type from malignant to benign or intermediate∗ was recognized.
The results suggest that HM bacilli infection induced higher level of cell-mediated immune reaction to M. lepraemurium than HB bacilli infection in the hosts.

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