Pathophysiology of autoimmune bullous diseases

Spectrum of autoimmune vesiculobullous diseases in Iran: a 13-year retrospective study

BACKGROUND

Autoimmune bullous diseases (ABDs) represent a group of rare, acquired disorders characterized by overlapping features with involvement of the skin and mucous membranes, resistance to treatment, and potential lethality that comprise pemphigus, bullous pemphigoid (BP), epidermolysis bullosa, dermatitis herpetiformis, and linear immunoglobulin A bullous dermatosis.

AIM

The main aim of this study was to identify the epidemiologic characteristics and clinical courses of these common diseases in Hamadan, Iran. Few surveys have been carried out to demonstrate the whole spectrum of ABDs in the literature. Notably, in Hamadan we are the first.

MATERIALS AND METHODS

This 13-year retrospective study was designed to evaluate all of documented data obtained from hospitalized patients with ABDs at Farshchian Hospital from October 1999 to October 2012. We collected information on epidemiologic data, clinical aspects, histologic findings, and therapy prescribed. Data were analyzed using SPSS.

RESULTS

Of 168 patients, 78% had pemphigus. The age of patients at presentation ranged from 1 month to 115 years, with a mean of 47.5±19.93 years. Mucosal or skin involvement of ABDs was statistically significant (P<0.001). The incidence of ABDs differed significantly based on anatomic location (P=0.003). We documented three deaths.

CONCLUSION

Compared to previous literature, our findings showed equal epidemiologic properties in Iran. Although pemphigus was the most common ABD followed by BP, it is expected that in line with the global trend, an increase in BP will be driven by population aging in Iran.

Follicular helper T Cells (Tfh) and IL-21 involvement in the pathogenesis of bullous pemphigoid

The pathogenesis of bullous pemphigoid (BP) is characterized by the T cell-dependent production of autoantibodies. Recent studies have indicated that follicular T helper cells (Tfh), the key modulator of B cell activation and autoantibody production, are critical in the development of several autoimmune diseases. Tfh cells perform their functions via IL-21, their hallmark cytokine. In the present study, the frequencies of Tfh cells were investigated in the peripheral blood samples of BP patients to evaluate whether Tfh cells involve in this clinical entity. Significantly higher Tfh cell counts were observed in the peripheral blood of BP patients than those in healthy controls (median: 11.25% vs. 4.95%, respectively; P<0.001). Additionally, the serum IL-21 levels in BP patients were higher than those of the healthy controls (median: 103.98 pg/mL vs 46.77 pg/mL, respectively; P<0.001). The frequencies of Tfh cells and IL-21 levels were both positively correlated with anti-BP180-NC16A autoantibody titers (R = 0.712, P<0.01 and R = 0.578, P = 0.030, respectively). After effective therapy, the frequencies of Tfh cells as well as the serum IL-21 levels in BP patients decreased along with clinical improvement. Most importantly, Tfh depleted CD4(+) T cells and anti-IL-21 neutralization antibody could inhibit the T cell-induced B cell activation and secretion of BP autoantibody in vitro. Those results suggest that Tfh cells play an important role in autoantibody production and are involved in the pathogenesis of BP.

Collagen XVII (BP180) modulates keratinocyte expression of the proinflammatory chemokine, IL-8

Collagen XVII (COL17), a transmembrane protein expressed in epidermal keratinocytes (EK), is targeted by pathogenic autoantibodies in bullous pemphigoid. Treatment of EK with anti-COL17 autoantibodies triggers the production of proinflammatory cytokines. In this study, we test the hypothesis that COL17 is involved in the regulation of the EK proinflammatory response, using IL-8 expression as the primary readout. The absence of COL17 in EK derived from a junctional epidermolysis bullosa patient or shRNA-mediated knockdown of COL17 in normal EK resulted in a dysregulation of IL-8 responses under various conditions. The COL17-deficient cells showed an abnormally high IL-8 response after treatment with lipopolysaccharide (LPS), ultraviolet-B radiation or tumor necrosis factor, but exhibited a blunted IL-8 response to phorbol 12-myristate 13-acetate exposure. Induction of COL17 expression in COL17-negative EK led to a normalization of the LPS-induced proinflammatory response. Although α6β4 integrin was found to be up-regulated in COL17-deficient EK, siRNA-mediated knockdown of the α6 and β4 subunits revealed that COL17's effects on the LPS IL-8 response are not dependent on this integrin. In LPS-treated cells, inhibition of NF-kappa B activity in COL17-negative EK resulted in a normalization of their IL-8 response, and expression of an NF-kappa B-driven reporter was shown to be higher in COL17-deficient, compared with normal EK. These findings support the hypothesis that COL17 plays an important regulatory role in the EK proinflammatory response, acting largely via NF-kappa B. Future investigations will focus on further defining the molecular basis of this novel control network.