IL-4 signaling through polymorphic IL-4R alpha and the role of bone marrow derived macrophages in a murine model of allergic asthma

Interleukin-4 (IL-4) is a multifunctional cytokine that plays a role in the regulation of immune responses through its interaction with two types of IL-4 receptor complexes. Both types of IL-4 receptors utilize the IL-4Ralpha chain that contains high affinity for IL-4. IL-4Ralpha chains expressing the I50, V50, Q576R, or S503P (I50-, V50-, Q576R-, and S503P-IL-4Ralpha) single polymorphisms and a double mutation consisting of S503P and Q576R (S503P/Q576R-IL-4Ralpha) have been associated with altered IL-4 signaling in lymphocytes and with allergy in humans with conflicting results.; To analyze signaling through polymorphic IL-4Ralpha chains, human monocytic U937 cells were transfected with murine IL-4Ralpha of C57BL/6 origin that was mutated to generate polymorphisms analogous to those found in the human IL-4Ralpha in patients. STAT6 phosphorylation was analyzed in transfected U937 cells that were cultured in the continuous presence of murine IL-4 or after a pulse and washout. In the continual presence of IL-4, STAT6 phosphorylation levels were similar in S503P/Q576R-, I50-, and V50-IL-4Ralpha U937 cells. In an IL-4 pulse and washout, STAT6 phosphorylation was prolonged in V50-IL-4Ralpha U937 cells when compared to I50- and S503P/Q576R-IL-4Ralpha U937 cells. This prolongation of STAT6 phosphorylation was abrogated in cells treated with either a Jak inhibitor or an anti-IL-4Ralpha chain blocking antibody producing a STAT6 activation profile comparable to cells expressing the 150 polymorphism. This suggests that the prolongation of STAT6 phosphorylation in V50-IL-4Ralpha U937 cells is regulated by repeated IL-4 signaling. However, a correlation between the prolongation of STAT6 activation in cells expressing the V50 polymorphism and functional outcomes including CD23, MHC class II, and acidic mammalian chitinase expression and IL-4 inhibition of IFN-gamma induced STAT1 activation was not found in these cell lines.; IL-4Ralpha expression on bone marrow derived and non-bone marrow derived cells contributes to the severity of eosinophilic infiltration in a murine model of allergic asthma. Expansion of cells expressing the MHC class II molecule, IAd, IL-4Ralpha, and CD11b in OVA challenged mice indicates the possible role of the monocyte in the development of allergic asthma. To determine the role of CD11b positive cells in the asthma response, CD11b positive cells were developed in vitro from BALB/c Rag2 knockout and BALB/c IL-4Ralpha/Rag2 double knockout bone marrow and injected into BALB/c IL-412alpha/Rag2 double knockout mice. TH2 cells were provided exogenously. Mice that received CD11b positive cells developed from BALB/c RAG2 knockout mice showed an increase in the recruitment of eosinophils in the lung after challenge with ovalbumin as compared to mice that received CD11b positive cells developed from BALB/c IL-4Ralpha x RAG2 knockout mice. Furthermore, there was an increase in cells expressing the macrophage markers F4/80 and Ym-1 recruited to the lungs of mice that received CD11b positive cells developed from BALB/c Rag2 knockout mice. These results suggest that stimulation through the IL-4Ralpha on macrophages contributes to the development of the inflammatory response in allergic asthma.