Mechanisms of Acquired Immunity in Leishmaniasis

Leishmania species use sandflies as their vector, and it is in the sandfly that the promastigote stage develops. Development of the amastigote stage occurs within the macrophage. The three categories of leishmaniasis are cutaneous, mucocutaneous, and systemic leishmaniasis. Studying immunological control in leishmaniasis has been advanced by the use of mouse strains that are susceptible to most of the pathogens that infect humans. Leishmania donovani is the best Leishmania species to perform studies of immunology on because all grades of the disease ranging from self-healing cutaneous lesions to fatal visceral leishmaniasis can be observed with the same organism (Howard et al. 1984).

By analyzing at a large range of clinical and experimental studies, the case of acquired resistance to leishmaniasis via cell-mediated immunity is a common explanation for acquiring immunity to leishmaniasis. Humoral antibody responses are directly related to the severity of the infection, but there’s no evidence of the correlation of antibodies in determining the intensity of infection. C57BL/6 mice, which are inbred strains of mice commonly used in experimental studies, are innately resistant to many forms of leishmaniasis. Low intensities of parasites are detected after exposure, however, several months after parasite exposure the amount of leishmaniasis causing parasites increase locally and lead to cutaneous lesions. Despite exposure to lymphokine, macrophages fail to kill off the parasites. This mechanism of evasiveness is still being studied (Howard et al. 1984).

Some protection against less aggressive leishmaniasis, such as leishmaniasis caused by Leishmania tropica, can be induced in resistant mice with ultrasonicated promastigotes, but attempts to protect against more severe Leishmania species such as Leishmania donovani have not been as successful. However, after injecting irradiated and live L. donovani in different groups of mice, a trend of higher levels of cytotoxic T cells were detected in mice that showed very little signs of infections. More adoptive transfer experiments were performed and have established that T cells play a role in the protection induced by infection. Further evidence from other studies performed by other researchers also shows that T cells are capable of engaging in lymphokine-mediated activation of macrophages against Leishmania infection (Howard et al. 1984).

This article relates to the study by Guevara et al. (1994) “Presence of Leishmania braziliensis in blood samples from cured patients or at different stages of immunotherapy” because Guevara et al (1994) studied the presence of a Leishmania species in humans after being treated for the infection and Howard et al. (1984) researched how the infection could possibly be naturally fought against and to have a built immunity against infection.

Citation

J. Howard and F. Liew, 1984, Mechanisms of Acquired Immunity in Leishmaniasis, Phil. Trans. R. Soc. Lond., 307: 87-98

-Kaitlin Smith