Pediatric Rheumatology Online Journal → August 2003 →  Immunodeficiency Syndromes → Abstract #165

ISOLATION OF IMMUNE COMPLEXES IN CHILDREN FROM FAMILIES WITH PARTIAL C4 DEFICIENCY

T. L. Moore,¹ S. Kamat,¹ J. M. Low,¹ A. K. Chauhan.¹

¹Pediatric Rheumatology, Saint Louis University, St. Louis, MO

Objective: To analyze isolated immune complexes (IC) and complement levels (C') in children from two families with partial C4 deficiency.
Methods: We identified the children of two families with multiple members with partial C4 deficiency. Children of ages 7, 12, and 17 in the first family and ages 11 and 16 in the second family. A retrospective chart analysis was performed. We recorded information on clinical presentation, physical findings, and laboratory studies which included ANA, ANA profile, C3, C4, CH5O, C4 allotyping, sedimentation rate, rheumatoid factor, and chemistries. The total IC and fixed C3 and C4 were measured by Fc receptor based ELISA. The IC were purified by Fc receptor affinity chromatography and were subsequently analyzed on SDS-PAGE for immunoglobulin and complement content.
Results: By C4 allotyping, four of our patients' C4 phenotype was A3Q0B1 (the 12 and 17 year-old of first family), two were A3B2Q0 (the 11 and 16 year-old from the second family), and one was A3B1Q0 (the 7 year-old from the first family). Within the same families, both C4A and C4B deficiencies were noted. The overall load of IC in the serum was found to be low when compared to patients with autoimmune diseases. The IC, which were captured, displayed C3 and C4 within the complexes. Measurement of C4 by ELISA also showed adequate levels of C4 fixed in the IC. SDS-PAGE analysis revealed various gel bands.
Conclusions: The identification of two families with multiple members with partial C4 deficiency gave us the ability to study isolated IC from their sera. Within each family, deficiencies in both structural loci of C4A and C4B were noted. Though these patients have low levels of serum C4, they seem to have adequate levels of fixed C4 within their IC. SDS-PAGE analysis revealed a unique pattern. Thus, further studies in these children would be necessary to understand whether partial C4 deficiency patients use alternate mechanisms for more efficient processing of IC and therefore delay onset of autoimmune disease.