Collagen VI encodes antimicrobial activity: novel innate host defense properties of the extracellular matrix

Abstract

Collagen type VI is a subepithelial extracellular matrix component in airways and an adhesive substrate for oral pathogens [Bober et al.: J Innate Immun 2010;2:160-166]. Here, we report that collagen VI displays a dose-dependent antimicrobial activity against group A, C, and G streptococci by membrane disruption in physiological conditions. The data disclose previously unrecognized aspects of the extracellular matrix in innate host defense.

Fig. 1

Collagen type VI microfibrils induce killing of group A streptococcus by membrane destabilization. Antibacterial activity assay with S. pyogenes and collagen VI. AP1 bacteria were incubated with different concentrations of collagen VI for 2 h at 37°C. Bacteria incubated with TBS buffer or with LL-37 served as negative or positive controls, respectively (a). Molar concentrations are indicated in the figure. The dots represent individual experiments with the respective strain. b–d Negative staining and transmission electron microscopy of streptococcal membrane destabilization upon incubation with collagen VI. Initially, collagen microfibrils assemble at the bacterial surface (b). The globular von Willebrand A domains of collagen VI are often observed close to the bacterial surface (asterisks). Subsequently, membrane blebbing (c, arrowheads) and exudation of cytoplasmic content are visible (c, arrows). Large scale membrane disruption (d) finally leads to destruction of the bacteria cells (e). Scale bar = 100 nm.

Fig. 2

Correlation between bacterial killing efficiency and expression of M1 surface protein. a Incubation of S. pyogenes wild-type strain AP1 and isogenic mutants BMJ11, BMJ27.6, and BMJ71 with 1 µM collagen VI, followed by quantification of survival (cfu) in an antibacterial activity assay. In control samples bacteria were incubated with TBS buffer or LL-37. The dots represent individual experiments with the respective strain. b Specimens were analyzed by negative staining and electron microscopy. Scale bar = 1 µm. Mutants lacking M1 protein (BMJ11 and BMJ71) are less prone to growth inhibition (a) and membrane destabilization (b, arrowheads) than wild-type AP1 and the protein H mutant BMJ27.6.

Fig. 3

Dose-dependent killing of group A, C, and G streptococci by collagen VI. Electron microscopy of different streptococcus species after incubation with TBS (upper panel), 10 nM collagen VI (middle panel), or 2 µM collagen VI (lower panel). Group A streptococci (GAS), group C streptococci (GCS), and group G streptococci (GGS) are indicated in the figure. All different streptococci are killed by collagen VI in a dose-dependent manner by membrane permeabilization and cytoplasmic exudation. Scale bar = 1 µm.