THU0617 Is the number of igg4+ plasma cells seen by immunostaining useful beyond its diagnostic utility in igg4-related disease?
Authors: E. Martin Nares, J. Guerrero Castillo, A. Angeles Angeles, G. Hernández Molina
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> The histopathological findings in IgG4-related disease (IgG4-RD) includes the presence of marked IgG4 +plasma cell infiltration seen by immunostaining and it has been used in clinical practice only as a diagnostic tool. Whether the number of IgG4 +plasma cells in tissue is associated with any clinical or serological feature of the disease has not been previously evaluated. <h3>Objectives</h3> To evaluate if the number of IgG4 +plasma cell infiltration is associated with any clinical or serological outcome. <h3>Methods</h3> We included 30 patients with biopsy proven IgG4-RD according to the Comprehensive Diagnostic Criteria for IgG4-RD who regularly attended a tertiary referral centre in Mexico City (2000–2017). We collected demographics, clinical (organ involvement, relapses and the disease activity assessed by the IgG4-RD Responder Index [IgG4-RD RI] at baseline) as well as baseline laboratory data (C3, C4, total eosinophil count, IgG4 levels). Patients were divided in three groups according to the number of IgG4 +plasma cells seen by immunostaining as follows:&lt;50 IgG4 +plasma cells/HPF, 50–100 IgG4 +plasma cells/HPF, and &gt;100 IgG4 +plasma cells/HPF. <h3>Results</h3> We included 30 patients, 17 (56.6%) women, mean age 53±13.9 years and median disease duration 13 months. The biopsies were from the following tissues: lacrimal gland (n=6), pancreas (n=5), orbit (n=4), kidney (n=4), lymph node (n=3), mediastinum (n=2), salivary gland (n=2) and other tissues (n=4). Eleven patients (36.6%) had &lt;50 IgG4 +plasma cells/HPF, 9 patients (30%) 50–100 IgG4 +plasma cells/HPF and 10 (33.3%) patients&gt;100 IgG4 +plasma cells/HPF. We did not find any difference regarding age, gender, time of follow up, number of involved organs and relapses. The median basal IgG4-RD RI was 9, 6 and 15, for the &lt;50 IgG4 +plasma cells/HPF, 50–100 IgG4 +plasma cells/HPF, and &gt;100 IgG4 +plasma cells/HPF groups respectively, however, they did not reach statistical significance. The group with &gt;100 IgG4 +plasma cells/HPF had more frequently lymphadenopathy when compared with the other groups (36.4%, 66.7% and 80%, p=0.02; respectively) while the proportion of involvement of the other anatomic sites were similar. We found a statistical difference in serum C3 levels (99.5 mg/dl, 159 mg/dl, 78.5 mg/dl, p=0.04) and a tendency for serum C4 levels (20 mg/dl, 27 mg/dl, and 6 mg/dl, p=0.08) among the groups, whereas the levels of serum IgG4 (60.8 mg/dl, 196 mg/dl, 245 mg/dl, p=0.35) and the eosinophil count (284/mm<sup>3</sup>, 189/mm<sup>3</sup>, 283/mm<sup>3</sup>, p=0.46) were similar. The C3 and C4 serum levels negatively correlated with the basal IgG4-RD RI (<b>τ</b>=−0.48, p=0.005 and <b>τ</b>=−0.58, p=0.001). <h3>Conclusions</h3> Our results show that the number of IgG4 +plasma cells seen by immunostaining in IgG4-RD may be of value in identifying a subset of patients with hypocomplementemia, lymphadenopathy and probably higher basal disease activity. The finding of an association between hypocomplementemia and higher tissue infiltration by IgG4 +plasma cells expands the evidence that complement activation may contribute to the pathogenesis of IgG4-RD. <h3>Reference</h3> [1] Carruthers M, Stone J, Deshpande V, et al. Development of an IgG4-RD Responder Index. Int J Rheumatol2012;2012:259408. <h3>Acknowledgements</h3> No acknowledgements to report. <h3>Disclosure of Interest</h3> None declared