The B-cell superantigen Finegoldia magna protein L causes pulmonary inflammation by a mechanism dependent on MyD88 but not B cells or immunoglobulins.

Objective And Design: To determine whether Finegoldia magna protein L (PL) causes lung inflammation and, if so, whether the response is dependent on its immunoglobulin (Ig)-binding B-cell superantigenic property.

Material: Pulmonary inflammatory reactions were analyzed at various time points after intratracheal administration of PL to various strains of mice.

Results: PL caused peribronchial and perivascular inflammation that peaked at 18-24 h. Polymorphonuclear cells (PMNs) began to accumulate in bronchoalveolar lavage fluid (BALF) of PL-challenged mice by 4 h and accounted for >90% of leukocytes by 18-24 h. Inflammation was marked by the appearance of MIP-2, KC, TNF-α, and IL-6 in the BALF with peak levels attained 4 h after PL administration. PL-induced pulmonary inflammation was associated with increased airway hyper-reactivity following inhalation of methacholine. The inflammatory reaction was unabated in mice lacking B cells and immunoglobulins. In contrast, PL-induced inflammation was abrogated in MyD88-deficient mice. PL-induced responses required alveolar macrophages.

Conclusions: These results strongly suggest that PL-induced lung inflammation is dependent on an innate MyD88-dependent pathway rather than the Ig-binding properties of this microbial B cell superantigen. We propose that this pulmonary inflammatory reaction is caused by the interaction of PL with a Toll-like receptor expressed on alveolar macrophages.