Blood cytotoxic/pro-inflammatory mediators in severe asthma

Non-Eosinophilic Asthma (NEA) is a distinct inflammatory subtype for which there are no effective treatments. NK and NKT-like cells are a small but important proportion of effector lymphocytes that, like CD28null T-cells, are relatively resistant to steroids and a major source of pro-inflammatory/cytotoxic mediators in COPD. We hypothesized that similar findings are present in NEA. Patients with severe asthma, participating in a multi-center RCT comparing add-on azithromycin with fixed-dose maintenance therapy, had increased airflow variability and were poorly controlled despite maintenance therapy with inhaled GCS. In eosinophilic asthma (EA), NEA, and controls (20/group), we applied flow cytometry to measure blood T, CD28null, NK and NKT-like cells, their expression of the cytotoxic inhibitory receptor CD94(Kp43), activation (CD69), cytotoxic potential(granzyme B, perforin, CD158 and CD107A) and intracellular pro-inflammatory cytokines (TNFα and IFNγ). In NEA there was significantly increased expression of NK cytotoxic markers vs controls (eg, CD158: 132% increase) and T-cell granzyme B (71 % increase). TNF-a and IFN-g production by NK and NKT-like cells were also significantly increased in NEA vs EA. In both asthma phenotypes there were significant changes in CD4+28null T-cells (72% and 81% increase respectively vs controls), CD94 (NEA: 35% decrease for NK and 26% for NKT-like cells),activation (CD69 increased on T and NKT-cells), granzyme B (increased in CD4+28null vs CD4+28+ T-cells) and production of TNF-a and IFN-g (all subsets). The increased pro-inflammatory/cytotoxic lymphocytes, especially in NEA, are likely to contribute to disease severity and steroid resistance, and provide a therapeutic target.