Production of interleukin-12 by murine macrophages in response to bacterial peptidoglycan

Abstract

Peptidoglycan (PG), a component of the bacterial cell wall, has various immunomodulating activities, including the capacity to induce delayed-type hypersensitivity reactions to antigens administered in Freund's adjuvant. We report that PG induces interleukin-12 (IL-12) mRNA production and IL-12 secretion by mouse macrophages. The capacity of PG to induce IL-12 production, like its previously reported immunomodulating activities, was dependent on the structure of its peptide subunit. PG from Bacillus megaterium and Staphylococcus aureus induced IL-12 production, whereas PG from Micrococcus luteus and Corynebacterium poinsettiae did not. The ability of most bacterial PGs to induce IL-12 production suggests that they play an important role in triggering host defense mechanisms against bacterial infections.

FIG. 1

Induction by B. megaterium PG of IL-12 p40 mRNA in the J774 macrophage cell line. Macrophages were incubated with the indicated concentrations (micrograms per milliliter) of LPS or PG from B. megaterium. Unstimulated macrophages were used as a control. Total RNA was extracted at the indicated times, reverse transcribed, and amplified by PCR with primers specific for IL-12 p40 and β-actin. Amplified products were submitted to agarose gel electrophoresis and stained with ethidium bromide. M, molecular size markers.

FIG. 2

Correlation between PG structure and the ability to induce IL-12 p40 mRNA. Macrophages were incubated for 24 h with the indicated concentrations of LPS or with PG from B. megaterium (B. meg.), S. aureus (S. aur.), C. poinsettiae (C. poin.), and M. luteus (M. lut.). IL-12 p40 and β-actin mRNAs were amplified as described in the legend to Fig. 1. Results are representative of three experiments. M, molecular size markers.

FIG. 3

Effect of lysozyme digestion on the capacity of PG from B. megaterium to induce IL-12 mRNA production in J774 cells. RT-PCR was carried out after 24 h of incubation. Lanes: 1, control; 2, LPS (10 μg/ml); 3, PG from B. megaterium (100 μg/ml); 4, PG from B. megaterium (100 μg/ml after lysozyme digestion). M, molecular size markers.