PO042-WEN Anti-ADAMTS13 antibody features (IG isotype titers, functional ADAMTS13 inhibitor and circulating immune complexes [CIC]) in patients with acquired thrombotic thrombocitopenic purputa (aTTP) at first consultatio in our institution

KEMPFER AC; PAIVA-PALOMINO J; SÁNCHEZ LUCEROS A; ALBERTO MF; WOODS AI; CASINELLI MM; LAZZARI MA

Toronto

Congreso; XXV Congress of the International Society on Thrombosis and Haemostasis and 61st Annual SSC Meeting.; 2015

International Society on Thrombosis and Haemostasis

Background: aTTP form is often caused by circulating antibody (ab).The formation of CIC may be a pathophysiologic mechanism inaTTP.Aims: To evaluate the relationship of ADAMTS13-measurements in40 patients (P), 28 in acute phase (ap) and 12 non acute phase (nap).Methods: ADAMTS13 activity (act), antigen (ag) and Free IgG anti-ADAMTS13 ab (free IgG ab) were evaluated by ELISA kits. FunctionalADAMTS13 inhibitor (FI) was detected as Ferrari (2007)described. Detection of CIC by co-immunoprecipitation (WB) andELISA with rabbit anti-ADAMTS13 (ABCAM). Informed consentand ethical approval were obtained.Results: In ap, act was severely reduced in 26/28P (93%) and reducedin 2/28P (7%). Within 26P Ag was undetectable in 7 (27%), severelyreduced in 3 (11%) and reduced in 14 (54%). FI was positive in 24/28P(86%). Free IgG ab was positive in 24/28P (86%). In nap, act wasseverely reduced in 3/12P (25%) and reduced in 6/12P (50%). Withinthose 12P, ag was severely reduced in 1 (8%) and reduced in 6 (50%).FI was positive in 8/11P (73%). Free IgG ab was positive in 10/12P(83%). Both Free IgM ab and IgA ab were positive in 1/12P (8%).The capturing ab for CIC showed good sensitivity when tested using aP with a CIC of cut-off of 1.93 normalized OD units. The nonparametriccorrelation n = 9, Spearman r = 0.695, P < 0.04 between CICELISAand WB was significant (a=0.05). In ap, CIC was detected in 9/28P, in 8/26P with severe act deficiency the prevalence of CIC was33% (95% CI, 16?50%) and in 1/28P with reduced act. Within those9P, the ag was undetectable in 2P, severely reduced in 2P and reducedin 4P; free IgG ab in 5P and positive FI in 8P. In naP, CIC wasdetected in 3/12P and in 2/6P with reduced act the prevalence of CICwas 40% (95% CI, 9?70%). Within those 3P ag was reduced in 2, freeIgG ab in 2P and negative FIConclusion: Only one-third of P with aTTP displayed CIC. If the determinationof circulating CIC in a first consultation is of value in predictingpotential relapse will be further investigated increasing thenumber of P with aTTP.