Pathological roles of MRP14 in anemia and splenomegaly during experimental visceral leishmaniasis

Myeloid-related protein 14 (MRP14) belongs to the S100 calcium-binding protein family and is expressed in neutrophils and inflammatory macrophages. Increase in the number of MRP14+ cells or serum level of MRP14 is associated with various diseases such as autoimmune diseases and infectious diseases, suggesting the involvement of the molecule in pathogenesis of those diseases. In this study, to examine the pathological involvement of MRP14 during cutaneous and visceral leishmaniasis, wild-type (WT) and MRP14 knockout (MRP14KO) mice were infected with Leishmania major and L. donovani. Increase in the number of MRP14+ cells at the infection sites in wild-type mice was commonly found in the skin during L. major infection as well as the spleen and liver during L. donovani infection. In contrast, the influence of MRP14 to the pathology seemed different between the two infections. MRP14 depletion exacerbated the lesion development and ulcer formation in L. major infection. On the other hand, the depletion improved anemia and splenomegaly but not hepatomegaly at 24 weeks of L. donovani infection. These results suggest that, distinct from its protective role in CL, MRP14 is involved in exacerbation of some symptoms during VL.
Author summary Inflammatory responses are crucial in limiting pathogen infections, whereas they often have detrimental effects to the hosts during infectious diseases. Thus, exploring molecules involved in inflammatory responses and targeting those molecules may contribute to development of novel interventions for symptom management during infectious diseases. Although an inflammation-related protein, MRP14, is associated with a wide range of inflammatory diseases, the functions remain elusive. Therefore, we explored the roles of MRP14 in a protozoan disease called leishmaniasis because its pathology is known to be immune-mediated. Interestingly, in two distinct forms of leishmaniases, i.e., cutaneous leishmaniasis caused by Leishmania major and visceral leishmaniasis caused by L. donovani, the molecule showed distinct roles in protection/pathology; although the molecule was protective against L. major infection, depletion of the molecule resulted in easing the pathology during L. donovani infection. These may prove the complexity of MRP14, but at the same time support understanding of the mechanisms behind the complexity.