Abstract
During canine visceral leishmaniasis (CanL), due to Leishmania infantum (L. infantum), uncontrolled infection leads to a strong humoral immune response. As a consequence of the production of high antibody levels and the prolonged presence of parasite antigens, circulating immune complexes (CIC) are formed, which can be deposited in certain organs and tissues, inducing vasculitis, uveitis, dermatitis and especially glomerulonephritis and renal failure. A method to detect CIC and quantify their levels in serum samples from dogs infected with L. infantum has been recently described. It allowed demonstration of a correlation between CIC levels and disease severity. Thus, CIC measurement may be useful for diagnosis, assessment of disease progression and monitoring response to treatment. This is an interesting finding, considering that there remains an urgent need for identification of novel biomarkers to achieve a correct diagnosis and for optimal disease staging of dogs suffering from Leishmania infection. The objective of the present review is to shed light on the role of CIC in CanL, as well as to highlight their potential use not only as diagnostic and prognostic biomarkers but also as a valuable tool in vaccine development and new immunotherapy strategies to prevent or control disease outcome.
Highlights
Leishmaniases are a group of parasitic diseases caused by different species of the Leishmania parasite
Canine visceral leishmaniasis (CanL), caused by Leishmania infantum (L. infantum), is a global zoonotic disease that is potentially fatal for dogs and, due to its potential transmission, to humans
This study demonstrated a clear correlation between circulating immune complexes (CIC) levels and pathologic stage in animals infected with L. infantum
Summary
Leishmaniases are a group of parasitic diseases caused by different species of the Leishmania parasite. Microorganisms 2021, 9, 712 extent, complement system fractions [15] Macrophages activated by these immune complexes inhibit IL-12 biosynthesis, and, IFN-γ production, and secrete high levels of IL-10 [16], impeding the establishment of cell-mediated immunity and reducing the macrophage’s ability to kill the parasite [14]. Veterinarians should use information from multiple sources, such as clinical history; examination findings; clinicopathological abnormalities; molecular tests to detect the parasite, such as the Polymerase Chain Reaction (PCR); and serological tests to evaluate the host immune response, such as the immunofluorescence antibody test (IFAT) or the Enzyme-Linked ImmunoSorbent Assay (ELISA) This evaluation is necessary to characterize the severity of the disease and determine the clinical stage, enabling the selection of an adequate treatment or to predict progression toward more serious and irreversible stages [19,20]. The goal of this review is to summarize what constitutes the state-of-the-art regarding the role of CIC in CanL and to postulate how the analysis of these molecules can provide interesting biomarkers to gain more information about new players for diagnosis, prognosis and treatment of the disease
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