Paradoxically, however, patients with lepromatous (Virchowian) HD, the most severe and transmissible form, have no skin reaction to the antigen.
Lepromatous HD, the more severe and disfiguring form is a result of the patient's immune response being mainly humoral in nature.
Antibodies, the main effectors of a humoral response, are ineffective against M. leprae because of the unusually dense and waxy nature of the mycolic acid containing bacterial cell wall, and so the bacterium proliferates, causing the cutaneous disfigurements and peripheral neuropathologies characteristic of the disease.
The Fernandez (early) reaction appears within two days and is roughly equivalent in nature and underlying mechanism to the response seen in tuberculosis patients reacting positively to the tuberculin test.
Unlike the tuberculin test, however, another reaction occurs in lepromatous patients at the injection site 21 days post-injection, also appearing as induration and possible ulceration.
[citation needed] Aldo Castellani was the first to prepare a substance similar to lepromin while attempting to produce a leprosy vaccine.
[6][7] Kensuke Mitsuda worked with lepromin starting in 1916 and published the first paper on it in 1919[8] However, he retained Ernest Reinhold Rost's earlier name leprolin and his original idea was to find a test that distinguishes leprosy patients from non-leprosy persons.
[9] Working on Java in the Dutch East Indies, Paul Bargehr published his findings on a similar process in 1926, giving his modified serum the name lepromin.