Inositol metabolism in mononuclear leucocytes from patients with atopic dermatitis

Impaired Toll-like receptor 2-mediated Th1 and Th17/22 cytokines secretion in human peripheral blood mononuclear cells from patients with atopic dermatitis

BACKGROUND

Impaired Toll-like receptor 2 (TLR2) function has been associated with the pathogenesis of atopic dermatitis (AD). However, there are only few studies reporting on the TLR2-induced immunological responses of circulating leucocytes of AD patients. We thus investigated the expression and secretion of Th1, Th2 and Th17/22 cytokines triggered by TLR2 ligands in human peripheral blood mononuclear cells (PBMCs) from AD patients. Expression of TLR2, 1, 6 and high-affinity receptor for IgE (FcεRI) were further investigated to evaluate the outcome of immune response in AD.

METHODS

Expression of TLR2, 1, 6 and FcεRI in PBMCs from AD patients and healthy individuals were measured by qPCR. Subsequent to stimulation with TLR2 ligands PGN and Pam3CSK4, expression and secretion of Th1, Th2 and Th17/22 cytokines were investigated by qPCR and ELISA.

RESULTS

The levels of TLR2, 1, 6 mRNA were not altered in both groups of subjects while that of FcεRI was increased in AD patients. Subsequent to the activation by TLR2 ligands, PBMCs from AD patients significantly released less IFN-γ, IL-17F and IL-22 than those from healthy controls while no detectable level of release was observed with the other cytokines. In contrast, significantly higher levels of mRNA expression for TNF-α, IL5, IL-17A and IL-22 were observed in TLR2 activated PBMCs of AD patients than those of healthy control.

CONCLUSIONS

PBMCs from AD patients are defective in the secretion of Th1 and Th17/22 cytokines in response to TLR2 ligands. The inconsistent increased expression of the mRNA for the corresponding Th1 cytokines and the Th2 cytokines IL-5 suggested that there may be alterations of downstream signaling events in the cytokine release mechanisms of PBMCs that are associated with the development of AD.

Enhanced procoagulant activity of mononuclear leukocytes in patients with atopic dermatitis and psoriasis

Fibrin deposition is an important histopathological feature of inflammatory skin lesions and is mediated in part, by procoagulants generated by mononuclear leucocytes (MNL). We examined whether MNL from patients with atopic dermatitis or psoriasis generate enhanced procoagulant activity (PCA). MNL isolated from the peripheral blood of 15 healthy control individuals, 15 patients with atopic dermatitis and 15 patients with psoriasis were incubated for 24 h in the presence or absence of bacterial lipopolysaccharide (LPS). MNL or the cell culture supernatants were then added to recalcified human plasma to determine the clotting time. We found that in both atopic dermatitis and psoriasis MNL cultured in the presence or absence of LPS expressed greatly enhanced PCA (p < 0.01 to < 0.002). Supernatants from MNL cultures from patients with psoriasis, but not those from patients with atopic dermatitis, also generated augmented PCA (p < 0.002). In psoriasis, PCA normalized after successful topical treatment with anthralin. We conclude that enhanced PCA is a characteristic feature of MNL in both atopic dermatitis and psoriasis. In psoriasis the enhanced PCA is directly related to disease activity.

Atopic dermatitis--messengers, second messengers and cytokines

Atopic dermatitis (AD) shows many complex and interacting abnormalities of pharmacology, immunology and cellular control. Recent research in atopy has concentrated on abnormalities of cytokine production by T-helper cells. It is possible that cytokine imbalance causes many of the pharmacological and immunological changes seen in the disease. However, studies of second messenger control of cytokine release show that different second messenger signals may relate to the release and activation of particular cytokines. This review summarizes these findings and discusses how the second messenger defects reported in AD may relate to the abnormal cytokine profiles and the pharmacological abnormalities seen in the condition.

Measurement of phosphoinositide-specific phospholipase C activity in mononuclear leucocytes from atopic and normal subjects

The intracellular inositol pathway is an important route for cell activation and relies on the stimulation of membrane-bound phosphoinositide-specific phospholipase C (PLC). Previously we have shown abnormalities of inositol metabolism in mononuclear cells (MNL) in atopic dermatitis (AD) using an indirect method. We now describe a direct method of measuring PLC activity in membrane and cytosol preparations of MNL in AD. We compare PLC activity in AD with that in normal controls and examine the effect of substrate concentration and nucleotide stimulation on the system. Our findings show increased membrane-bound PLC activity in AD compared with normal controls. Non-specific stimulation of AD PLC activity by nucleotides suggests that the enzyme of atopics is more sensitive to substrate-driven activity than that of non-atopics.