In vitro production of a biologically active Fab2-like fragment by digestion of human IgG rheumatoid factor with human polymorphonuclear leukocyte elastase

Quantification and evaluation of the role of antielastin autoantibodies in the emphysematous lung

Chronic obstructive pulmonary disease (COPD) may be an autoimmune disease. Smoking causes an imbalance of proteases and antiproteases in the lung resulting in the generation of elastin peptides that can potentially act as autoantigens. Similar to COPD, Z alpha-1 antitrypsin deficiency (Z-A1ATD) and cystic fibrosis (CF) are associated with impaired pulmonary antiprotease defences leading to unopposed protease activity. Here, we show that there is a trend towards higher bronchoalveolar lavage fluid (BALF) antielastin antibody levels in COPD and Z-A1ATD and significantly lower levels in CF compared to control BALF; the lower levels in CF are due to the degradation of these antibodies by neutrophil elastase. We also provide evidence that these autoantibodies have the potential to induce T cell proliferation in the emphysematous lung. This study highlights that antielastin antibodies are tissue specific, can be detected at elevated levels in COPD and Z-A1ATD BALF despite their being no differences in their levels in plasma compared to controls, and suggests a therapeutic role for agents targeting these autoantibodies in the lungs.

The biological properties of immunoglobulin G and its split products [F(ab')2 and Fab]

Antibodies of the IgG class possess antibacterial, antiviral and toxin neutralizing properties and for this reason are administered prophylactically and therapeutically. In the case of the immunoglobulin preparations commercially available for i.v. application a basic distinction must be made between unsplit immunoglobulins and those antibody preparations obtained by enzymatic digestion, such as F(ab')2 or Fab antibodies. This survey deals with the largely experimental evidence describing the biological properties of these preparations. Administration of antibodies in the presence of the corresponding antigens leads to the formation of immune complexes in the organism. These immune complexes can activate, either directly or indirectly, the cellular and humoral systems which are involved in phagocytosis and the elimination of antigens, in the regulation of the body's own antibody production and in inflammatory reactions. As a result of their inability to interact with Fc receptors, immune complexes with F(ab')2 or F(ab) antibodies appear to be less active in the release of inflammation mediators from leucocytes and thrombocytes than immune complexes with unsplit immunoglobulins. These, on the other hand, can antigen-specifically and non-antigen-specifically suppress the immune system which is not the case for immune complexes with F(ab')2 or Fab antibodies. There are indications that these split products also occur in vivo due to the action of tissue and leucocyte proteases. Unlike Fab preparations, F(ab')2 antibodies have antibacterial and antiviral potencies similar to unsplit immunoglobulins, which is probably due to the ability of F(ab')2 molecules to activate complement, not by the classical but by the alternative pathway. Like Fab preparations, F(ab')2 molecules appear to be superior to unsplit IgG in the elimination of haptens. On account of the relatively long period of time unsplit immunoglobulins remain in the blood, they are well suited for prophylactic treatment and substitution over longer periods. The extent to which indications, obtained predominantly from experimental studies, of a reduced release of inflammation mediators, a lack of immune suppression and a lack of augmentation of IgG catabolism would advocate the use of F(ab')2 split products, especially for therapeutic purposes, can only be ascertained after prospective and comparative studies have been carried out.

Cathepsin G from human polymorphonuclear leukocytes cleaves human IgM

Cathepsin G, the chymotrypsin-like enzyme from human polymorphonuclear leukocytes, cleaves human IgM and produces two major fragments that closely resemble those released by leukocyte elastase digestion of IgM. An F(ab)2 mu-like fragment, mol. wt 140,000, retains some reactivity with an anti-Fc mu antiserum and is antigenically deficient with respect to the IgM subunit. The other fragment is an Fab mu-like product with a mol. wt of 54,000. Both cathepsin G fragments are indistinguishable from the elastase counterparts by immunochemical analysis. An Fc mu fragment could not be recovered. The kinetic course of the cleavage shows that cathepsin G produces Fab mu fragments at a higher rate than F(ab)2 mu, whereas the contrary is valid for elastase. Beside the two major fragments and low mol. wt peptides, cathepsin G releases also a product with the same mol. wt and immunological reactivity as the IgM subunit. The biological significance of the interaction between IgM and leukocyte proteinases is discussed.

A comparative analysis of human IgM rheumatoid factor degradation by purified elastase and total granule extracts from human polymorphonuclear leukocytes

A modified digestion system using radiolabeled IgM rheumatoid factors (RF) and unlabeled IgG was used to examine IgM RF digestion by human polymorphonuclear leukocyte (PMN) elastase. Upon molecular sieve chromatography, the radioactive fragments coelute with fragments produced by elastase digestion of an IgM protein giving no RF activity. The fragments represent an Fab2-like fragment, an Fab-like fragment, and small peptides. Utilizing this same system, digests were performed at both acid and neutral pH to compare the proteolytic action of purified elastase on IgM RF (Ove) to the action of the total granule extract (TGE) from human PMN. At pH 4.5, purified elastase exhibits low-level protease activity, producing a slightly degraded IgM fragment with a molecular weight of about 800,000 daltons. In contrast, TGE at pH 4.5 completely degrades IgM RF to small peptides. At pH 7.5, the fragments produced by TGE digestion of IgM (Ove) coelute with fragments produced by elastase digestion under the same conditions. Thus elastase appears to be the major granule protease active in IgM RF degradation at the pH characterizing the inflammatory site.