Different Propionibacterium acnes Phylotypes Induce Distinct Immune Responses and Express Unique Surface and Secreted Proteomes

Abstract

Propionibacterium acnes is a skin commensal bacterium that contributes to the development of acne vulgaris and other infections. Recent work revealed that P. acnes clinical isolates can be classified into distinct phylotypes, several of which have associations with healthy skin or acne. We sought to determine if these phylotypes induce different immunological responses and express protein factors that may contribute to their disease associations. We found that acne-associated P. acnes phylotypes induced 2- to 3-fold higher levels of IFN-γ and IL-17 in peripheral blood mononuclear cells compared with healthy phylotypes. On the other hand, P. acnes phylotypes associated with healthy skin induced 2- to 4-fold higher levels of IL-10. Comparative proteomic analysis of P. acnes phylotypes revealed a differential expression of several proteins, including an adhesion protein that was expressed at least 10-fold higher in acne-associated phylotypes and a cell surface hydrolase expressed in all phylotypes except those associated with healthy skin. Taken together, our data provide insight into how specific P. acnes phylotypes influence immune responses and the pathogenesis of acne.

Figure 1.. Exponential phase Propionibacterium acnes induces a greater Th1 response and stationary phase P. acnes induces a greater Th17 response.

A total of 2.5 × 10⁶/ml peripheral blood mononuclear cells were cultured with 2.5 × 10⁶/ml live P. acnes. ELISA was conducted on the supernatant to determine the concentration of IFN-γ, IL-17, and IL-10. The level of cytokine secretion for exponential and stationary phase P. acnes is plotted for (a) IFN-γ, (b) IL-17, and (c) IL-10. Data are from one of five similar experiments. Statistics show t-test comparisons between exponential and stationary phase values. *P < 0.05, **P < 0.01, ***P < 0.001. p±, presence or absence of a large plasmid; RT, ribotype; Th1, T helper type 1; Th17, T helper type 17.

Figure 2.. Phylotypes of Propionibacterium acnes induce distinct cytokine immune response patterns.

A total of 2.5 × 10⁶/ml peripheral blood mononuclear cells were cultured with 2.5 × 10⁶/ml live P. acnes in the exponential phase for (a) IFN-γ or the stationary phase for (b) IL-17 and (c) IL-10. ELISA was conducted on the supernatant to determine the concentration of IFN-γ, IL-17, and IL-10. Data are from one of five similar experiments. Statistics show t-test comparisons with the maximum two-way P value between the phylotype groups indicated. *P < 0.05, **P < 0.01, ***P < 0.001. p±, presence or absence of a large plasmid; RT, ribotype.

Figure 3.. Cytokine induction patterns are similar across multiple donors.

A total of 2.5 × 10⁶/ml peripheral blood mononuclear cells were cultured with 2.5 × 10⁶/ml live Propionibacterium acnes in the exponential phase for (a) IFN-γ or the stationary phase for (b) IL-17 and (c) IL-10. ELISA was conducted on the supernatant to determine the concentration of IFN-γ, IL-17, and IL-10. The cytokine concentrations normalized to the highest value induced by any P. acnes strain for each donor and cytokine. Each donor is represented by a different symbol. p±, presence or absence of a large plasmid; RT, ribotype.

Figure 4.. Immunological clustering of phylotypes.

Propionibacterium acnes phylotypes were clustered with an average-distance city-block method using ELISA results for IFN-γ, IL-17, and IL-10. p±, presence or absence of a large plasmid; RT, ribotype.