SLPI, Human, mAb 31

The monoclonal antibody 31 recognizes secretory leukocyte proteinase inhibitor (SLPI).
SLPI was identified as an alarm reactant and expression is induced by inflammatory factors
like LPS, IL1β, TNFα and neutrophils elastase. SLPI is a relatively small basic antiprotease
of 11.7 kDa and is a cationic non-glycosylated protein consisting of 107amino acids. SLPI
has a high affinity for the neutrophil serine proteinases, elastase and cathepsin G.
Orthologues of SLPI have been found in mice, rate, pigs and sheep. It consists of two highly
similar WAP (‘whey acid protein’)/four-disulphide core domains. SLPI contain 16 cysteine
residues which assemble into eight disulphide bridges (four in each WAP domain). SLPI is
constitutively expressed at many mucosal surfaces and is produced by a variety of epithelial
cells, including respiratory, intestinal and amniotic epithelia. Expression is also detected in
mast cells, neutrophils and macrophages. Expression of SLPI gene is significantly
increased by progesterone and by the pro-inflammatory cytokines TNF-α and IL1-β.
Although SLPI has been shown to inhibit a spectrum of proteases (including HNE,
cathepsin G, trypsin, chymotrypsin and chymase), its main action in this regard is likely to
be the inhibition of elastase, as indicated by its low dissociation constant and favourable
kinetics of inhibition for this enzyme. SLPI has been described in several body fluids like
seminal fluid, bronchial fluids, cervical fluids and saliva. It has been found to be
antibacterial, antifungal, anti-retroviral, and to have an important role in mucosal defence.
SLPI might also facilitate tumor spread, contributing to wound healing, is elevated in sepsis
and levels seem to correlate with oral candidiasis in HIV-1 positive patients. The reactivity of
the antibody 31 with isolated domains of SLPI was evaluated using domains obtained by
cleavage using partial acidic hydrolysis. Therefore, monoclonal antibody 31 recognizes also
other SLPI cleavage products.