Introduction Serine proteinases such as proteinase 3 (PR3) and neutrophil elastase (NE) on the surface of activated neutrophils retain their activity, which may be central to the tissue damage in emphysema. However, little is known about this expression in A1ATD when it may be more critical.

Aims

1. To compare neutrophil surface expression of PR3 and NE in patients with A1ATD, usual COPD and healthy controls.

2. To determine the influence of the local concentration of A1AT on neutrophil surface expression of PR3 and NE.

Methods Clinically stable patients with A1ATD (n=9), COPD (n=6) and healthy controls (n=9) were recruited. Neutrophils were isolated from blood. Half were stimulated with fMLP and half were unstimulated. Membrane expression of NE and PR3 was measured by flow cytometry.

Neutrophils isolated from six further healthy controls were stimulated in the presence of either normal (PiMM) or A1ATD plasma (PiZZ). Membrane expression of NE and PR3 was measured.

Results PR3 expression on the surface of unstimulated neutrophils was greater in A1ATD patients (2365±305MFI) compared to healthy controls (1517±253MFI; p=0.048) and COPD patients (1360±315MFI; p=0.046). NE expression was similar between groups.

PR3 expression on stimulated neutrophils was greater in A1ATD patients (5112±547MFI) compared to healthy controls (3411±541MFI; p=0.042), but not different to COPD patients (4723±1509MFI; p=0.78). NE expression was similar between groups.

When neutrophils from healthy controls were stimulated in the presence of plasma, the surface expression of PR3 (but not NE) was greater (p=0.031) in the presence of PiZZ plasma (1921MFI) compared to PiMM plasma (1352MFI), but less than that observed without plasma.

Conclusions Baseline neutrophil surface expression of PR3 is greater in A1ATD patients compared to healthy controls. Neutrophils express more PR3 when stimulated in an environment with low concentrations of A1AT, suggesting that membrane binding is dependent on the ability of A1AT to bind released PR3 but not NE.

This may have clinical significance for A1ATD emphysema since active membrane-bound PR3 is resistant to inhibitors and can replicate the pathological features associated classically with NE.

These findings may explain the association of Wegener’s granulomatosis (where PR3 is an autoantigen) with A1ATD.