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Immunity in leprosy
Last reviewed: 04.07.2025
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Most healthy people develop relative natural immunity to leprosy mycobacteria, which is characterized by a fairly high intensity. The state of the macroorganism's immunological reactivity to the leprosy pathogen is determined mainly by cellular immunity reactions. The intradermal lepromin test is most often used for this purpose. Positive results of this test indicate a pronounced ability of the organism to develop a response to the introduction of leprosy mycobacteria, i.e. a high degree of natural immunity. A negative response indicates suppression of cellular immunity reactions, in other words, the absence of natural immunity.
Therefore, the degree (strain) of natural immunity is one of the decisive factors in a person's immunity to leprosy and the formation of the type of leprosy infection in case of infection. Individuals with a positive Mitsuda reaction are significantly less susceptible to the risk of contracting leprosy. If infected, the disease proceeds more favorably (usually in the form of tuberculoid leprosy) and may end in self-healing. Individuals with a negative Mitsuda reaction are a high-risk group. If infected, the disease proceeds more malignantly (usually in the form of lepromatous leprosy) and may have an unfavorable outcome.
Natural immunity to leprosy is relative, since its degree (tension) can change under the influence of various factors. Due to repeated infection (superinfection) with leprosy, concomitant diseases, hypothermia and other reasons, the tension of natural immunity can weaken to the point of complete suppression. Measures aimed at increasing the body's defenses and the use of the BCG vaccine help to strengthen natural immunity to leprosy.
According to most authors, humoral immunity factors do not have a protective effect in leprosy.
[ Pathogenesis of leprosy
Mycobacterium leprae penetrates the human body mainly through mucous membranes, less often through damaged skin, without causing visible changes at the site of introduction. Then the pathogen slowly spreads into tissues and organs through nerves, lymphatic and blood vessels.