Department of Infectious Diseases and Department of Clinical Microbiology, State University Hospital, Institute of Medical Microbiology, University of Copenhagen, Biomedical Sciences Research Centre and Clinical Research Centre, Kenya Medical Research Institute, Department of Tropical Diseases, University of Amsterdam, Walter and Eliza Hall Institute of Medical Research, Copenhagen, Denmark
In a cross-sectional house-to-house study in a leishmaniasis-endemic area in Kenya, the cellular and humoral immune response to Leishmania lipophosphoglycan (LPG) was determined. Clinical data, peripheral blood mononuclear cells, and plasma were obtained from 50 individuals over the age of eight years. Lymphoproliferation and interferongamma (IFN-γ) production by these cells were examined. It was shown that cells from all six individuals in the population with a history of kala-azar responded to LPG in the lymphocyte proliferation assay, and four of these six responded in the IFN-γ assay. In contrast, cells from 12 of 44 individuals from the study area with no history of kala-azar and none of the five Danish control samples responded to LPG. Antibodies against LPG were detected by enzyme-linked immunosorbent assay in 45 of 50 plasma samples. Our findings clearly show that mononuclear cells from kala-azar patients cured of infection were able to respond to the LPG preparation. The finding of a specific cellular immune response to LPG in 12 of 44 individuals with no history of kala-azar is consistent with previous epidemiologic studies, in which it has been shown that a proportion of L. donovani infections run a subclinical course. The high frequency of individuals with antibodies against LPG might indicate that a majority of the population had been exposed to the parasite. The soluble L. donovani antigen gave rise to proliferation and IFN-γ production in cell samples from all individuals with a history of kala-azar, in three of five cell samples from Danish controls with no known exposure to Leishmania, and in 36 of 44 samples from members of the study population with no history of kala-azar. In contrast, the response to LPG seemed highly specific.