Cryoglobulins, rheumatoid factors and connective tissue disorders

Practical Details for the Detection and Interpretation of Cryoglobulins

BACKGROUND

Cryoglobulins are immunoglobulins that precipitate at low temperature. Strict preanalytical and analytical conditions are critical for the detection of cryoglobulins.

CONTENT

This review will focus on practical recommendations for detection and characterization of cryoglobulins and the technical problems that may be encountered. A laboratory report format is proposed for presentation of these results that includes the parameters necessary for an optimal interpretation by clinicians. The first step of detection of cryoglobulins can be performed in any laboratory that has a 37 °C incubator and temperature-controlled centrifuge. The second step is the characterization of cryoglobulins, and this often must be performed in more specialized laboratories. Characterization includes immunoglobulin typing, for the classification of cryoglobulins and potential underlying disease(s); quantification of immunoglobulins and rheumatoid factor in the cryoprecipitate to define the pathogenicity; and quantification of serum complement, which is useful for diagnosis.

SUMMARY

These practical recommendations will be useful for the accurate detection of cryoglobulins, an essential step for the diagnosis of cryoglobulinemic vasculitis, a rare but severe clinical manifestation of cryoglobulins.

Cryoglobulinemic vasculitis: pathophysiological mechanisms and diagnosis

PURPOSE OF REVIEW

Cryoglobulins (CG) are immunoglobulins that precipitate in the cold, and dissolve at 37°C. In vivo, in cold exposed tissues and organs, they can induce vasculitis and occlusive vasculopathy after deposition on vascular endothelium under low temperature and high concentration conditions. Clinical manifestations are cutaneous (purpura, ulcers, vasomotor symptoms, and livedo reticularis), rheumatological (arthralgia and arthritis), and peripheral neuropathy (paresthesia and pain in the lower limbs). In profound organs such as the kidneys, CG deposition is less temperature-dependent, favored by local protein and anion concentrations, and can lead to glomerulonephritis. This review will focus on cryoglobulinemic vasculitis and vascular lesion, and their diagnosis.

RECENT FINDINGS

The mechanisms of vascular lesions of pathogenic CG in function of CG type and their characteristics are better defined. Optimal conditions for CG detection are critical. The importance of looking for underlying diseases, especially hepatitis C virus status in mixed CG, is reminded.

SUMMARY

A decision diagram for CG vasculitis diagnosis based on clinical and biological parameters is proposed.

Hypertrophic osteoarthropathy, cutaneous vasculitis, and mixed-type cryoglobulinemia in a patient with nasopharyngeal carcinoma

We describe a 27-year-old woman with a primary nasopharyngeal carcinoma who developed hypertrophic osteoarthropathy and cutaneous vasculitis. Her serum contained antibodies to Epstein-Barr virus and U1 RNP antigens. Cryoproteins isolated from her serum contained antibodies to U1 RNP and a protein with a molecular weight of 32 kd which reacted specifically with antibodies to U1 RNP. HLA typing revealed HLA-B7 and DR1; these have been reported to be increased in Japanese patients with rheumatic diseases who have autoantibodies to U1 RNP. These findings indicate that some features of the paraneoplastic syndrome in this patient might have been caused by immune complexes, part of which were formed by specific autoantibodies produced under genetically controlled conditions of immune responsiveness.

Immunopathology of coeliac disease

Coeliac disease may be defined as a condition in which there is an abnormal jejunal mucosa with loss of villi, which improves morphologically after treatment with a gluten-free diet. Pathologically, there is damage to the jejunal enterocytes, with hyperplasia of crypt cells so that overall enteropoiesis is increased. On conventional or scanning electron microscopy the enterocytes are markedly abnormal. Histochemically, the normal punctate appearance of the lysosomes is lost and sensitive lysosomal enzyme assays on mucosal biopsy samples using isopycnic centrifugation techniques show that there is an increase in total lysosomal activity with reduction in lysosomal latency. Studies following gluten feeding in patients whose mucosa has returned to normal after treatment with a gluten-free diet show that pathological abnormalities appear within 4--8 hours of gluten challenge. Complement together with extracellular IgM can be demonstrated in the lamina propria, suggesting the formation of immune complexes. In untreated coeliac disease there is a significant reduction in serum levels of C3 and C4. There is also evidence indicating the presence of immune complexes in the serum. Coeliac disease may therefore be an intestinal model of an immune complex disease, in which an antigen derived from gluten reacts with an antibody formed locally in the gut, fixing complement and causing damage to the enterocyte by activation of lysosomes.

Hereditary complement (C2) deficiency with dermatomyositis

A 60 year old white man in previous good health presented with a 6 month history of progressive muscle weakness. Clinical and laboratory findings were typical of dermatomyositis. Muscle biopsy confirmed the presence of inflammatory myopathy; deposits of immunoglobulin G (IgG), immunoglobulin M (IgM) or third component of complement (C3) were not detected by immunofluorescence. No evidence was found for an associated neoplasm. An unexpected finding was the total absence of serum hemolytic complement activity. Further investigation revealed that the complement defect was attributable to a selective and total absence of the second component of complement (C2), as determined by both functional and immunoprecipitin assays. Family studies indicated that the defect was inherited in an autosomal recessive manner, as has been observed in the previously reported C2-deficient kindreds. This case demonstrates that typical muscle lesions of dermatomyositis can occur in the presence of a complement defect which would preclude activation of the classic (C1-C4-C2) complement pathway. The case is of further interest as one of a series of recently reported associations of rheumatic diseases with hereditary complement deficiencies. Study of the functional properties of the propositus' C2-deficient serum demonstrated normal generation of chemotactic activity in the presence of endotoxin or aggregated IgG, and normal or near normal bactericidal activity against Salmonella typhi O 901 and Hemophilus influenzae, type b. These findings emphasize the importance of the alternate (properdin) pathway of complement activiation in these functions.