This paper reviews some recent studies which have been performed by us and other investigators, in order to clarify the reason why most mycobacterial infections such as due to Mycobacterium tuberculosisand M. avium complex infections are intractable, that is, why these organisms can escape from attack by microbicidal mechanisms of host macrophages and consequently persist for long time at sites of infection. This paper mainly dealt with the two major subjects, which were studied by using an experimental model for murine M. avium infection. The first subject is on the modes and mechanisms of mycobacterial killing in host macrophages and the mechanisms of bacterial escape from an onslaught by macrophages. The second is on the characteristics of immunosuppressive macrophages induced in M. avium complex infection and the role of the suppressor macrophages in the establishment of immune unresponsiveness of host mice in the progressed stage of infection.

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The author analyzed the results of cataract surgery performed in 25 eyes of 22 lep-rosy patients. All the eyes were treated by phacoemulsification-aspiration technique with intraocular lens implantation. The subjects consisted of 15 eyes of 14 leprosy patients with past history of uveitis and 10 eyes of 8 leprosy patients without uveitis. The mean follow-up time after surgery was 20 months and 23 months, respectively. In 93% of eyes with uveitis and 90% of eyes without uveitis, the postoperative vision im-proved by 2 lines or more. Postoperative complications were higher among patients with uveitis (93%) compared with patients without uveitis (40%). But no serious com-plications were encountered in patients with uveitis.

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Among the lesions caused by mycobacteriosis, peripheral neuropathy has been regarded as the pathognomonic one peculiar to leprosy which is caused only by M. leprae (ML) which can not be cultivated. If that whole sentence is correct, no past report should be in existence concerning the peripheral neuropathy caused by the experimental inoculation of certain cultivated mycobacterium and not of ML. There was, however, an exception challenging to that theory which was done by Sasaki et al. in 1985.
The author, therefore, tried to reproduce this type of lesion in the nude mice modifying their method to know whether a leproma-derived and cultivable mycobaceterium HI-75 (HI-75) still have the ability to cause neuropathy as they observed.
The mycobacterium utilized in the study was originally separated from a leproma by Skinsnes et al. as M. leprae (ML) HI-75 in 1975 and was identified as M. scrofulaceum (MS) by Stanford et al. in 1977. The strain was kept on cultivating in his laboratory till 1984 and in ours thereafter. The groups of mice served for the present experiments consisted of two. The mice in the first group were infected intravenously and those in the latter group were by subcutaneous injections in the cheeks mixed with hyaluronic acid. The first one was unsuccessful to make remark-able neuropathy, however, the second one showed the marked invasions of the bacilli in peripheral nerves encompassed by numerous macrophages which were heavily loaded with the mycobacteria.
The author believes that the present result is helpful to solve the question about the differences of the characteristics of HI-75 before and after causing neuropathy in vivo, the mutual relationship between ML, MS and HI-75 and the causative organism beside ML if present.

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The sequence of the polymerase chain reaction (PCR) product of 16S ribosomal RNA (16SrRNA) of the leproma-derived and cultivable Mycobacterium HI-75 (M. HI-75) was examined to obtain the knowledge of its taxonomic characteristics directly by dideoxy method. The sequence was most similar to that reported for Mycobacterium scrofulaceum (MS) with 0.5% differences in the sequenced 973 bases of 16S rRNA. The mycobacterium examined in this study was originally isolated as M, leprae (ML) by Skinsnes, et al. in 1975 from leproma of a lepromatous type Hansen's disease patient and therefore named as Mycobacterium leprae HI-75 (M. HI-75) by them. The claim was denied by Stanford, et al. in 1976 who reported the identity of HI-75 as MS. The bacillus was maintained in the second author's laboratory from 1984 using either Ogawa's or Sauton's media in the beginning and Ogawa's medium enriched with glucuronic acid and N-acetyl-D-glucosamine recently. During that period of time Sasaki reported the nerve invasion and the growth of the inoculated bacilli either to the nude mice or the I¹³¹ immunocompromized Swiss mice. This episode provoked a doubt that there should be a missing link of knowledge between leprosy and M. scrofulaceum since the nerve invasion of the bacilli has been regarded rather as a characteristics of ML and not that of MS. In addition to that the other genomic study about HI-75 performed by Williams by PCR and restriction flagment length polymorphism (RFLP) suggested the resemblance of the bacilli as either M. smegmatis or M. fortuitum and not MS (1994, pers. comm.). Those raised the question whether M. HI-75 has changed during the cultivation for 21 years. The 16SrRNA obtained from the strain by the present study indicated that M. HI-75 still preserve some characters of MS. The result should be consonant with that by Stanford et al. 19 years ago and thereby suggesting the maintenance of the original characteristics at that time. Therefore the present study indicated the missing link of the knowledge between ML, its nerve invasion and MS which should be brought into elucidation in future by the analytical study awaring the possibility that ML might transform genomically in vivo or MS beside ML might invade and grow in the nerve.

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