Immune Activation in α1-Antitrypsin-Deficiency Emphysema. Beyond the Protease–Antiprotease Paradigm

B Cell-Activating Factor. An Orchestrator of Lymphoid Follicles in Severe Chronic Obstructive Pulmonary Disease

RATIONALE

Patients with chronic obstructive pulmonary disease (COPD) have increased pulmonary lymphoid follicle (LF) counts. B cell-activating factor of tumor necrosis factor family (BAFF) regulates B cells in health, but its role in COPD pathogenesis is unclear.

OBJECTIVES

To determine whether BAFF expression in pulmonary LFs correlates with COPD severity, LF size or number, and/or readouts of B-cell function in LFs.

METHODS

We correlated BAFF immunostaining in LFs in lung explants or biopsies from nonsmoking control subjects (NSC), smokers without COPD (SC), and patients with COPD with the number and size of LFs, and LF B-cell apoptosis, activation, and proliferation. We analyzed serum BAFF levels and BAFF expression in B cells in blood and bronchoalveolar lavage samples from the same subject groups. We assessed whether: (1) cigarette smoke extract (CSE) increases B-cell BAFF expression and (2) recombinant BAFF (rBAFF) rescues B cells from CSE-induced apoptosis by inhibiting activation of nuclear factor-κB (NF-κB).

MEASUREMENTS AND MAIN RESULTS

Patients with Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage IV COPD had increased numbers and larger pulmonary LFs than patients with GOLD stages I-II COPD and SC. We identified two main types of pulmonary LFs: (1) type A, the predominant type in GOLD stages I-II COPD and SC, characterized by abundant apoptotic but few BAFF-positive cells (mostly B cells); and (2) type B, the main type in GOLD stage IV COPD, characterized by abundant BAFF-positive cells but few apoptotic cells (mostly B cells). BAFF levels were also higher in blood and bronchoalveolar lavage B cells in patients with COPD versus NSC and SC. Surprisingly, rBAFF blocked CSE-induced B-cell apoptosis by inhibiting CSE-induced NF-κB activation.

CONCLUSIONS

Our data support the hypothesis that B-cell BAFF expression creates a self-perpetuating loop contributing to COPD progression by promoting pulmonary B-cell survival and LF expansion.

The multiple facets of alpha-1-antitrypsin

Alpha-1-antitrypsin (AAT) is recognised as a potent inhibitor of serine proteinases. Genetic deficiency is associated with several neutrophilic diseases including severe emphysema. This is believed to reflect the loss of inhibition of neutrophilic serine proteinases that then result in local tissue damage (the proteinase/antiprotease hypothesis). In recent years the role of AAT in the control of inflammatory and immunological processes has become identified. Although in some instances this may reflect its ability to control pro-inflammatory effects of serine proteinases it has also become recognised that it has non proteolytic mediated functions. This poly functional role is starting to become recognised offering a possibility of its use as a therapeutic agent in many clinical disease areas. The current review explores both the traditional and non-traditional function of AAT through published literature.