Fræðigrein

A strong association has been found between complement and common connective tissue diseases, such as systemic lupus erythema and Henoch Schoenlein Purpura. This has led to the notion that the pathogenesis of such diseases may involve a defect in the safe disposal of immune complexes, which is mediated by complement. To bring further light on this subject, a sensitive assay was developed to measure the ability of serum to prevent immune precipitation. This assay was then employed to study various Icelandic patient groups, and a defect in this function of complement was found to be common in patients with systemic lupus erythematosus and systemic sclerosis. Partial deficiency in complement C4A (C4A*Q0) can not account for this defect, as it was not observed in patients with diabetes, gluten-sensitive enteropathy or autoimmune thyroiditis, in which C4A*Q0 is common. The defect is strongly correlated with anti-C1q antibodies. Further studies are needed to test the possible role of anti-C1q antibodies in the pathogenesis of immune complex disease.

Key words: complement, inflammation, immune complex disease.

Correspondence: Guðmundur Jóhann Arason,

garason@lsh.is

Fig. 1. Sensitivity of an assay for measuring prevention of immune precipitation (PIP). AU=arbitrary units. At standard conditions, there is a linear relationship between PIP activity and serum dilution (9).

Fig. 2. PIP is deficient in SLE regardless of disease activity. PIP was impaired in 74 SLE patients sampled consecutively at study initiation, compared with 46 RA patients and 102 blood donors. This defect was apparent also when 44 SLE patients were sampled during low disease activity (SLEDAI score <10). The lower limit of normal (2 SD) is denoted by a dotted line (10).

Fig. 3. Prevention of immune precipitation (PIP) in patients with systemic sclerosis (SSc) compared with blood donors. The dotted line denotes the 95% lower cut off limit (11).

Fig. 4. Prevention of immune precipitation in patients with gluten-sensitive diseases (GSD), autoimmune thyroid disease and insulin-dependent diabetes mellitus (IDDM). Open circles denote heterozygous and dotted circles homozygous C4A*Q0 carriers. Filled circles represent C4A*Q0 non-carriers. Patients with Hashimoto’s disease are marked with arrows (12).