Widespread matrix-produced neutrophils shield the skin

Antineuophilic properties of the skin and elastic Young’s modulus of wild-type mice studied by two-sided unpaired Student’s t-tests

Immune cells in the skin ‘cauterize’ open wounds and create ‘band-aids’ to prevent the spread of harmful bacteria and foreign molecules from injury sites, finds a study1 in mice.

Researchers examined the skin, lungs, and gut of a mouse, to see if they have another trick up their sleeves, in order to find out if they have another trick up their sleeves. Hidalgo and his colleagues found that a high percentage of neutrophils in these tissues produce collagen and other proteins that are important for forming ‘extracellular matrix’, a scaffolding that surrounds cells and gives tissues structure. By contrast, neutrophils in blood did not release collagen.

a, Representative images of neutrophils (green) stained for Col3a1 (red) in the skin of WT control (CreNEG Tgfbrflox littermates, 5 images from 2 mice) and TgfbrΔN mice (9 images from 3 mice), which we used to quantify the number of neutrophils per volume area is shown at right. Data are presented as mean values ± s.e.m., compared by two-tailed unpaired Student’s t-test. Hematoxylin-eosin staining for cell and tissue structure, Masson’s trichrome for collagen-rich structures, and Ki are some of the highlights of histonic characterization of the skin of wild-type control. There are dot plot graphs for images. The t-test was used to determine the P-values. In the table below you can see the distribution of width in the histogram, as well as in the extended data fig. 4A for control vs. iDTR mice). P-values were determined by a two-sided unpaired Student’s t-tests. The elastic Young’s modulus can be measured using the atomic force microscopy set up in tissue samples. Each dot represents the median Young’s modulus value calculated from ∼250 individual force–distance analysed curves per mouse. Data were compared by two-sided unpaired Student’s t-test. Right, representative height images and corresponding Young’s modulus maps of skin from control (n = 5) and TgfbrΔN littermates (n = 5) acquired by AFM indentation experiments. e, TEM images of the ear skin transversal sections showing collagen fibres in the subepidermal and lower dermis regions, which were automatically segmented for analysis (coloured fibres). Yellow circles highlight large collagen fibres (>0.2 μm2) in the subepidermal region. The data from 2 independent experiments were used to quantify fibre size in the TgfbrN mice and CreNEG littermates. The Kruskal-Wallis test determines the P-values. g, Per cent of ‘large’ fibres in the subepidermis and lower dermis from the images in f. Data are presented as mean values ± s.e.m., and p-values were determined by Kruskal-Wallis non-parametric test. h, Permeability assays in control (n = 7) and TgfbrΔN mice (n = 7) measured by FITC–dextran injected either intratracheally (for lung), or by oral gavage (for gut) in CreNEG control (n = 8) and TgfbrΔN mice (n = 8). The Evans blue was given to control and Tgfbr N mice and then measured in the indicated tissues. All controls here were Cre-negative Tgfbrflox littermates. i,j, Stiffness (i) and permeability assay (j) using Evans blue in the ear skin of Mrp8Cre; Tgfbr2flox and Ly6GCre; Tgfbr2flox mice, as well as CreNEG; Tgfbr2flox littermates, or mice treated with anti-Ly6G to deplete neutrophils or isotype control antibody. The numbers of replicates are displayed in the figure. P-values determined by two-sided Student’s t-test comparing each depletion method with their controls (left panels), or one-way ANOVA with multiple comparison test (right panels). The median interquartile is shown in box plots as well as whiskers. Box plots in f show median ± interquartile; whiskers are defined with percentiles and IQR (interquartile range, P75–P25); the points outside this range are the outliers.