Inbred Rats as a Model to Study Persistent Renal Leptospirosis and Associated Cellular Immune Responsiveness

Abstract

Pathogenic species of Leptospira cause leptospirosis, a bacterial zoonotic disease with a global distribution affecting over one million people annually. Rats are regarded as one of the most significant reservoir hosts of infection for human disease, and in the absence of clinical signs of infection, excrete large numbers of organisms in their urine. A unique biological equilibrium exists between pathogenic leptospires and reservoir hosts of infection, but surprisingly, little is known concerning the host's cellular immune response that facilitates persistent renal colonization. To address this deficiency, we established and applied an immunocompetent inbred rat model of persistent renal colonization; leptospires were detected in urine of experimentally infected rats by 3 weeks post-infection and remained positive until 8 weeks post-infection. However, there was little, if any, evidence of inflammation in colonized renal tubules. At 8 weeks post-infection, a robust antibody response was detected against lipopolysaccharide and protein outer membrane (OM) components. Purified B and T cells derived from the spleen of infected and non-infected rats proliferated in response to stimulation with 0.5 μg of OM fractions of Leptospira, including CD4+ T cells, which comprised 40% of proliferating cells, compared to 25% in non-infected controls. However, analysis of gene expression did not determine which immunoregulatory pathways were activated. Lymphocytes purified from the lymph node draining the site of colonization, the renal lymph node, also showed an increase in percentage of proliferating B and T cells. However, in contrast to a phenotype of 40% CD4+ T cells in the spleen, the phenotype of proliferating T cells in the renal lymph node comprised 65% CD4+ T cells. These results confirm that the renal lymph node, the local lymphoid organ, is a dominant site containing Leptospira reactive CD4+ T cells and highlight the need to consider the local, vs. systemic, immune responses during renal colonization infection. The use of inbred immunocompetent rats provides a novel tool to further elucidate those pathophysiological pathways that facilitate the unique biological equilibrium observed in reservoir hosts of leptospirosis.

Macrophages and Galectin 3 Control Bacterial Burden in Acute and Subacute Murine Leptospirosis That Determines Chronic Kidney Fibrosis

“…All experimentation in rats was conducted in accordance with protocols as reviewed and approved by the Animal Care & Use Committee at the National Animal Disease Center, and as approved by USDA Institutional guidelines. Female Fisher 344 inbred rats (Strain F344/NHsd, Envigo) of approximately 4 weeks of age were experimentally infected with 1 × 10 7 low-passage L. interrogans serovar Copenhageni as described (Nally et al, 2018 ).…”

Investigating the Immunological and Biological Equilibrium of Reservoir Hosts and Pathogenic Leptospira: Balancing the Solution to an Acute Problem?

“…Bovine neutrophils co-cultured with L. borgpetersenii (serovar Hardjo) also minimally produce Neutrophil Extracellular Traps (NET) compared to Escherichia coli and PMA controls (Wilson-Welder et al, 2016). In rats, gene expression of immune related genes in spleens of L. interrogans (serovar Copenhageni) challenged animals were nearly identical to the spleens on non-infected controls (Nally et al, 2018b). These observations exemplify the delicate immunological and biological equilibrium of persistent leptospirosis in reservoir hosts.…”

“…Outbred rats are routinely used to model persistent renal carriage (Tucunduva de Faria et al, 2007;Athanazio et al, 2008;RamachandraRao et al, 2015). Inbred rats (R. norvegicus) offer additional insights (Nally et al, 2018b); upon challenge with L. interrogans (serovar Copenhageni) inbred rats present asymptomatically, but kidneys become colonized and leptospires are shed in urine by 3 weeks, through at least 8 weeks, post challenge. Inbred rats developed robust antibody responses to leptospiral antigens, positive MAT titers, and showed prominent B cell proliferation when stimulated with leptospiral outer membrane proteins (Nally et al, 2018b).…”

“…Inbred rats (R. norvegicus) offer additional insights (Nally et al, 2018b); upon challenge with L. interrogans (serovar Copenhageni) inbred rats present asymptomatically, but kidneys become colonized and leptospires are shed in urine by 3 weeks, through at least 8 weeks, post challenge. Inbred rats developed robust antibody responses to leptospiral antigens, positive MAT titers, and showed prominent B cell proliferation when stimulated with leptospiral outer membrane proteins (Nally et al, 2018b). Interestingly, despite pathogen presence, the rats were largely void of lesion pathology in kidney tissue (including a lack of interstitial nephritis), and gene expression analysis of prominent T cell pathways between the spleens of infected and non-infected controls yielded few differences (Nally et al, 2018b).…”

“…Inbred rats developed robust antibody responses to leptospiral antigens, positive MAT titers, and showed prominent B cell proliferation when stimulated with leptospiral outer membrane proteins (Nally et al, 2018b). Interestingly, despite pathogen presence, the rats were largely void of lesion pathology in kidney tissue (including a lack of interstitial nephritis), and gene expression analysis of prominent T cell pathways between the spleens of infected and non-infected controls yielded few differences (Nally et al, 2018b). This suggests complex immune escape of the pathogen including limited immune activation from the host, however, activated lymphocytes including CD4+ were significantly expanded in the renal lymph nodes of infected animals compared to controls (Nally et al, 2018b).…”