Evidence of involvement of the mannose receptor in the internalization of Streptococcus pneumoniae by Schwann cells

Abstract

BackgroundThe ability of S. pneumoniae to generate infections depends on the restrictions imposed by the host’s immunity, in order to prevent the bacterium from spreading from the nasopharynx to other tissues, such as the brain. Some authors claim that strains of S. pneumoniae, which fail to survive in the bloodstream, can enter the brain directly from the nasal cavity by axonal transport through the olfactory and/or trigeminal nerves. However, from the immunological point of view, glial cells are far more responsive to bacterial infections than are neurons. This hypothesis is consistent with several recent reports showing that bacteria can infect glial cells from the olfactory bulb and trigeminal ganglia. Since our group previously demonstrated that Schwann cells (SCs) express a functional and appropriately regulated mannose receptor (MR), we decided to test whether SCs are involved in the internalization of S. pneumoniae via MR.ResultsImmediately after the interaction step, as well as 3 h later, the percentage of association was approximately 56.5%, decreasing to 47.2% and 40.8% after 12 and 24 h, respectively. Competition assays by adding a 100-fold excess of mannan prior to the S. pneumoniae infection reduced the number of infected cells at 3 and 24 h. A cytochemistry assay with Man/BSA-FITC binding was performed in order to verify a possible overlap between mannosylated ligands and internalized bacteria. Incubation of the SCs with Man/BSA-FITC resulted in a large number of intracellular S. pneumoniae, with nearly complete loss of the capsule. Moreover, the anti-pneumococcal antiserum staining colocalized with the internalized man/BSA-FITC, suggesting that both markers are present within the same endocytic compartment of the SC.ConclusionsOur data offer novel evidence that SCs could be essential for pneumococcal cells to escape phagocytosis and killing by innate immune cells. On the other hand, the results also support the idea that SCs are immunocompetent cells of the PNS that can mediate an efficient immune response against pathogens via MR.

PGL I expression in live bacteria allows activation of a CD206/PPARγ cross-talk that may contribute to successful Mycobacterium leprae colonization of peripheral nerves

“…Since CD206 was previously shown to be expressed by SCs [ 33 , 34 ], we then explored the ability of M . leprae or BCG PGL I to modulate this receptor.…”

Differential phagocytosis of Leishmania mexicana promastigotes and amastigotes by monocyte‐derived dendritic cells

“…Yeast mannan from S. cerevisiae displays mannose residues and is known to bind MR . It has previously been used as a positive control for the blocking of this receptor . We pre‐incubated moDCs with mannan for 1 hr before adding L. mexicana promastigotes.…”

Pneumolysin binds to the mannose receptor C type 1 (MRC-1) leading to anti-inflammatory responses and enhanced pneumococcal survival

“…MRC-1 binds to endogenous and microbial antigens such as capsular polysaccharides12,13. Furthermore, studies have demonstrated that MRC-1 influences pneumococcal uptake by Schwann and olfactory cells, but they did not show co-localization14,15. It is not clear which macrophage receptors recognize pneumococci in the nasopharynx and lungs and what bacterial properties interacts with the receptors mediating pneumococcal uptake.…”