A Novel Anti-Microfilament Antibody, Anti-135 kD, is Associated with Raynaud's Disease, Undifferentiated Connective Tissue Disease and Systemic Autoimmune Diseases

Abstract

We report herein the characterization of a human IgG antibody reactive with a nonmuscle 135 kD microfilament-associated protein, anti-135 kD. Using nonmuscle epithelial PtK2 cells as substrate in indirect immunofluorescence, we identified a distinctive pattern of reactivity with microfilaments in sera from 12 of 165 (7.3%) patients investigated for systemic autoimmune diseases and in only 2 of 171 (1.2%) normal and rheumatic disease controls (P < 0.006, 95% CI 1.46 to 30.1). An association between anti-135 kD and Raynaud's phenomenon (n= 12/14, 85.7%) with or without an associated systemic autoimmune disease was noted. The anti-135 kD specificity was established by several criteria. (1) The fluorescence was periodically distributed along microfilaments and concentrated at focal adhesions for all sera (n = 14). (2) On immunoblots, the 14 sera reacted with a PtK2 polypeptide of 135 kD. (3) IgC purified by blot-affinity from the 135 kD band (a-135) reproduced the fluorescent pattern of the original sera while IgG purified from other bands did not. (4) Double immunofluorescence with a-135 and anti-α-actinin mAb indicated absence of antibody fluorescence at ruffling membranes where α-actinin was distributed. (5) IgG subclass analysis of anti-135 kD revealed that 12 (85.7%) sera are of IgC3 isotype and 2 (14.3%) are of IgGl isotype while the light chain expression was K restricted. This is the first report of an antibody to a 135 kD microfilament protein. Anti-135 kD expand the repertoire of anti-microfilament and anticytoskeletal antibodies in human sera.

Key Words:

• anti-microfilament antibodies
• microfilament proteins
• antibodies
• autoimmunity
• Raynaud's phenomenon
• systemic sclerosis
• systemic lupus erythematosus
• polymyositis