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. 2022 Mar 28;13:841062. doi: 10.3389/fimmu.2022.841062

Figure 1.

Figure 1

Ficolin-2 specifically recognizes pneumococcal serotype 11A capsule polysaccharide (PS) and triggers lectin pathway-mediated opsonophagocytosis. (A) SIM fluorescent micrographs showing DRAQ5-stained nuclei (blue) and the surface location of either capsule antigens (first three columns, red) or bound ficolin-2 on bacteria incubated in 5% normal human serum (fourth column, green). Y-axis lists strains with respective capsule serotypes in parentheses, and X-axis lists detected structures. White scale bars depict 2µm. (B, C) Deposition of complement components C4 (panel B) and C3 (panel C) on MNY31 (black bars), MNY32 (white bars), and MNY33 (gray bars) incubated in C1Q/ficolin-2-depleted (ΔC1f2) serum, with or without recombinant ficolin-2 (rFicolin-2) and potential inhibitors (represented on X-axis tables). Surface bound complement is represented as log mean fluorescent intensity (MFI) measured by flow cytometry. (D) Survival of the aforementioned strains in an opsonophagocytic assay, represented as a percentage of the average bacterial load when heat-inactivated (H.I.) ΔC1f2 serum was used (first bar set). Panels B-D show the average value of three biological replicates in a single experiment representative of at least two separate experiments. Error bars depict two-fold standard deviations. Identity of inhibitors is shown on the bottom row of X-axis tables. aTC, anhydrous tetracycline; TA, teichoic acid; BSA, bovine serum albumin; acBCA, acetylated BSA; SCA, silica clot activator.