Levels of complement components during allergen-induced asthma

Role of the complement system in pulmonary disorders

Immune injury in the lung is classically divided into types I-IV hypersensitivity, with the complement system being involved in types II and III hypersensitivity. Anaphylaxis and asthma are generally considered prototypes of type I hypersensitivity and hypersensitivity pneumonitis as an example of type III hypersensitivity in the lung. However, in asthma, for example, increasing evidence indicates that in addition to mast cells, T lymphocytes play an important role. Therefore, considering asthma as strictly a type I mediated reaction is too simplistic. This report will review the evidence regarding the involvement of the complement system and complement activation products in anaphylaxis, asthma and immune complex disease in various experimental models of pulmonary disease. Identification of the mediators responsible for the symptoms may suggest rational targets for the continued development of effective therapy to combat immune injury in the lung.

The role of C5a in hypersensitivity reactions in the lung

What role the complement system in general, and C5a in particular play in hypersensitivity reactions in the lung is unknown. A review of the available studies indicates that C5a can mimic hypersensitivity reactions in the lung by virtue of its ability to cause cell infiltration and edema in the lung, cause a short lived airway hyperreactivity and cause bronchoconstriction. Its ability to cause contraction of isolated airways and in vivo bronchoconstriction in the guinea-pig is due to the release of histamine and arachidonate metabolites, mediator systems similar to those evoked by antigen-antibody reactions in the guinea-pig lung. To begin to determine if C5a generation with complement system activation was an important contributor to antigen-induced bronchoconstriction, the response to antigen was assessed in animals depleted of complement by cobra venom factor and unresponsive to C5a. Unexpectedly, these animals responded to antigen with a much greater bronchoconstriction than did animals with an intact complement system. This suggested that an intact complement system was somehow important in limiting allergic bronchoconstriction or conversely that allergic bronchoconstriction might be heightened when preceded by complement system activation. Thus, the data implicates C5a and/or complement system activation as a modulator of antigen-induced bronchoconstriction rather than directly contributing to the bronchoconstrictor component of hypersensitivity reactions in the lung.

Activation of the classical pathway of human complement in vitro by house-dust extracts is caused by IgM antibodies to polysaccharide antigen(s) and is not related to atopy

The mechanism of activation of the classical pathway of human complement by house-dust extracts and its relevance to atopic disease was studied. Our results confirm that for most sera of adults, house-dust extract is, on a weight basis, a more potent C-activator than aggregated human IgG or lipopolysaccharide (endotoxin). Naturally occurring IgM antibodies directed against ubiquitous polysaccharides appeared to be the dominant factor in the C1 activation by house-dust extracts in human sera. Large variations were found between sera with respect to the concns of these IgM antibodies as measured by C1 activation or fixation of haemolytic complement. The IgM antibody titre was, however, not associated with atopic disease. Consequently, we do not support the hypothesis put forward by Berrens et al. (1978) (Allergol. Immunopath. 6, 45-54) that there might be a relation between atopy and enhanced reactivity of serum complement with allergenic extracts. More than 90% of the C-activating potential of allergen extracts like house dust was found in the fractions with high mol. wt material (mol. wt greater than 100 K). Therefore, these antigens are easily separated from the known IgE-binding major allergens of house-dust mite and cat dander.

Late allergic bronchial reactions and the effect of allergen provocation on the complement system

Forty-nine bronchial provocations were performed with different allergens in allergic asthmatic patients. Immediate bronchial reactions occurred in 33 instances, and late reactions occurred in nine instances. The material was divided into three groups according to patients with no reactions, patients with early reactions alone, and patients with late reactions. Titers of whole complement and factors C2 and C3 were determined hemolytically, and the serum protein contents of factors C3, C4, and C1q were measured immunochemically. Decreases in complement and complement components were observed on a number of occasions after bronchial challenge. When the groups were compared with respect to mean change in complement titers, the three groups were indistinguishable. No change was noted in the ratio between the complement contents in venous and arterial blood as a result of provocation, nor did the specific hemolytic activity of factor C3 change. No C3 split products could be traced. It is likely that there will be a higher proportion of patients with C2 consumption among those with late bronchial reactions. No special feature could be assigned to these individuals, however. It is concluded that no major complement activation is regularly found in allergic asthmatic patients as a result of exposure to allergens. However, groups of patients in whom such activation takes place might exist.

Plasma histamine concentrations and complement activation during house dust mite-provoked bronchial obstructive reactions

Lung function and histamine levels in peripheral venous plasma samples were followed after challenge with house dust mite allergen. In eight patients the mean maximal histamine concentration showed a significant rise during the early obstructive reaction when compared with the concentrations at similar time intervals after inhalation of a control solution. In nine other patients treatment with disodium cromoglycate (DSCG) caused a significant fall in plasma histamine concentrations indicating that histamine liberation plays a role during the early obstructive reaction and was released from the lung compartment. Histamine during early obstructive reactions compared with the pre-inhalation values did show a rise in mean maximal histamine concentration (1.5-4.1 ng/ml) but this was statistically not significant. During the late reaction neither significant increase in histamine nor inhibition by DSCG was found. Measurement of complement degradation products did not support the role of complement activation during either early or late bronchial obstructive reactions.

Effect of house dust mite on serum complement activation and total haemolytic activity in vitro in normal subjects and in patients with bronchial asthma

House dust mite (Dermatophagoides farinae) has been shown to activate the complement system in vitro by both the classical and alternative pathways in normal serum and in two groups of (skin test positive and skin test negative) patients with bronchial asthma. The activation was dose dependent in the lower range of allergen concentrations. Skin test positive asthmatic subjects showed the maximum activation. Skin test negative patients had activation between skin test positive patients and normal subjects. However, at the higher allergen concentration normal serum and bronchial asthma patients showed similar results.

Studies on serum complement and IgE in bronchial asthma

Serum levels of the third component of complement (C3) were significantly lower in patients with perennial asthma and also in patients with the longer duration of the disease. No change in C3-proactivator (C3PA) and CH50 levels was observed in asthma patients. Significantly raised C4 levels were observed in the patients with late onset asthma. Raised serum IgE levels were found in all the three groups of asthma patients studied (depending on age of onset, duration and periodicity of the disease) above the control group. Within a group no difference was found with the duration or periodicity of the disease. However, low IgE levels were observed in patients with late onset asthma as compared to early onset asthma patients but this difference was not statistically significant.

Levels of complement factors in human serum during immediate and late asthmatic reactions and during acute hypersensitivity pneumonitis

In 16 asthmatic patients and in four subjects suspected of having hypersensitivity pneumonitis, serum levels of CH50, C3, C4, C5 and factor B were measured before, between 10 and 20 min, between 5 and 7 h and, in the latter group, also 24 h after allergen challenges provoking type I bronchial reactions or acute hypersensitivity pneumonitis. There was a significant decrease in one of the complement factors in two patients during the immediate asthmatic phase, but in no patient during the late asthmatic phase and in no patient with hypersensitivity pneumonitis. On the other hand, significant increases of C3, C4, and/or CH50 were seen in five patients during immediate asthmatic reactions, in seven patients during late asthmatic reactions and in all cases with hypersensitivity pneumonitis. However, with respect to the particular complement factors the vast majority of the patients showed no appreciable change. Investigations of C3 split products, which were done in seven patients gave negative results. No correlations existed between the changes in the levels of complement factors to increases of Raw, decreases of DLCO, size of skin test reactions or RAST scores. The cause and pathophysiological role of the non-uniform behaviour of serum complement levels after inhalation challenges is not yet clear; obviously both consumption and formation of complement factors take place during allergen-induced asthmatic reactions and hypersensitivity pneumonitis.

Circulating immune complexes in bronchial asthma

Soluble immune complexes were detected by a sold phase Clq binding assay in forty-two out of 106 well studied asthmatic patients (39.6%) and in eleven out of 145 age-matched controls (8%; P < 0.01). Clinical significance of immune complexes has been evaluated by comparing the following parameters in patients with and without such complexes: age, sex, duration of disease, IgE-mediated allergy (RAST, skin test), precipitins (Aspergillus, Candida albicans, Thermoactinomycetes), corticodependency, lung function tests, associated symptoms (hivernal bronchitis, urticaria, eczema,...), desenstization treatment, serum concentration in immunoglobulin in G, A, M and E. Immune complexes were found more frequently in female than in male patients. The prevalence of immune complexes was higher in patients treated by hyposensitization therapy and in cases with precipitating antibodies against thermophilic actinomycetes and Aspergillus.

Acute asthma compared with exacerbations of chronic bronchitis: changes in complement

Complement levels were measured on admission and at 1 and 7 days following admission in twenty patients with acute severe asthma and ten patients with an acute exacerbation of chronic bronchitis. Although no evidence of hypocomplementaemia was found in any patient, there was a mean fall within the normal range of the individual complement components, C4, C3 and factor B in both groups. The mean fall occurred earlier in the bronchitics than in the asthmatics and this may be related to infection or the administration of corticosteroids. There was a significant fall in C3 (P greater than 0.05) in the bronchitics compared with the asthmatics at 24 hr. From our study, however, we could find no evidence of excessive utilization of complement in acute asthma.