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Fig. 1 | BMC Ecology and Evolution

Fig. 1

From: Balancing selection on the complement system of a wild rodent

Fig. 1

Overview of the complement cascade. The cue to signal the complement cascade can be varied and helps determine the pathway that is activated. The classical pathway (CP) is primarily triggered when C1Q recognises and binds to the Fc region of antibodies or pentraxins bound to antigens. The lectin pathway (LP) is initiated when lectins of the complement system bind carbohydrates on cell surfaces. The alternative pathway (AP) is active constantly at low levels due to spontaneous hydrolysis of complement component C3, leading to indiscriminate C3b deposition on nearby cell surfaces. This is immediately cleared by regulators of complement activation (RCA) present on host cells, preventing complement activation. Microbes lack RCA proteins and thereby activate the alternative pathway. Thus, only the lectin pathway requires specific recognition of MAMPs. In all cases, C3 convertases are produced once the pathway is triggered which in turn cleaves complement component C5, with all pathways converging at this stage. Ultimately, a membrane-attack complex (MAC) is assembled and inserted on the pathogen surface, and this pore lyses the pathogen cell. In addition, complement activation leads to opsonization and activation of other inflammatory and immune pathways. The figure is for representative purposes and only a single role for complement proteins with multiple functions is presented here. Text in brown indicate genes that were not included in this study. Text in red indicate the gene with signature of balancing selection in the bank vole. Created with BioRender.com.

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