Single cell analysis of free cytosolic calcium changes in human lung mast cells--II. The relationship between desensitization and the cellular regulation of calcium changes

Recovery from desensitization of IgE-dependent responses in human lung mast cells

BACKGROUND

Clinical desensitization and oral food immunotherapy are therapeutic interventions that allow individuals who react adversely to an allergen (drug or food) to be made tolerant to the allergen. However, tolerance is brief, and allergen hypersensitivity can recur within days following allergen withdrawal.

OBJECTIVE

We hypothesize that the reason these treatments are temporary reflects rapid recovery of mast cells from a desensitized state. We sought to test this.

METHODS

Desensitization of IgE-mediated histamine release from human lung mast cells was explored by methods that partially replicate the pattern of treatment during clinical desensitization. Specific and non-specific desensitization and changes in surface IgE were examined following desensitization. Recovery from desensitization was also studied.

RESULTS

Desensitization of mast cell responses was readily induced with concentrations of antigen or anti-IgE that were suboptimal for secretion. There was little or no non-specific desensitization when lung mast cells were exposed to antigens. There was no loss of cell surface IgE following desensitization. Removing the desensitizing stimulus from the media following desensitization allowed the cells to recover with half-point of recovery of ~1.5 days and complete recovery after 5 days. Both the functional response and histamine content recovered within this time frame. The recovery appeared possible because both antigens and anti-IgE dissociated rapidly from cells after washing to remove excess stimulus.

CONCLUSIONS AND CLINICAL RELEVANCE

Human lung mast cells readily recover from a desensitized state following removal of desensitizing antigen. This finding provides a potential explanation for the ephemeral nature of clinical desensitization.

Allergen-specific conventional immunotherapy decreases immunoglobulin E-mediated basophil histamine releasability

BACKGROUND

Allergen-specific immunotherapy has proven to be clinically effective in the treatment of patients with atopic asthma; however, the mechanisms are still unclear. Several noted immunological changes include an increase of the allergen-specific IgG antibody, a reduction in the allergen-specific IgE antibody subsequent to transient increase, an allergen-specific T cell shift in cytokine production from Th2 to Th1, and a decrease in quantity and activity of basophils and mast cells.

OBJECTIVE

To analyse the changes of basophil histamine release in response to IgE-mediated and non-IgE-mediated stimuli before and after conventional house-dust mite immunotherapy in children who suffer from atopic asthma.

METHODS

Fourteen Dermatophagoides farinae (Df) sensitive asthmatic children with conventional immunotherapy were examined. Basophil histamine releasability was measured 0 months (just before immunotherapy), 4 months and 9 months after immunotherapy. Basophils were stimulated with Df and goat anti-human IgE antibody as IgE-mediated stimuli; and formyl-Met-Leu-Phe (fMLP) and calcium ionophore A23187 as non-IgE-mediated stimuli. Accordingly, the asthma symptom score was used to assess clinical outcome and the skin test reactivity to Df was measured.

RESULTS

In contrast to pre-immunotherapy activity, 4 and 9 months after immunotherapy there were significant decreases in histamine release by Df and by anti-IgE antibody. The histamine release by fMLP and by calcium ionophore showed no significant changes after immunotherapy. Histamine release by Df demonstrated significant correlation to that by anti-IgE antibody and by fMLP, yet there was no observable correlation between histamine release by Df and by calcium ionophore. The asthma symptom score decreased significantly 4 and 9 months after immunotherapy and showed significant correlation with histamine release by Df. The skin test reactivity (allergen/histamine ratio) remained constant 4 months after immunotherapy, but decreased significantly 9 months after immunotherapy.

CONCLUSION

Basophils have the potential to play an important role in the early clinical improvement of conventional immunotherapy in children with atopic asthma, which may be a result of the decreased IgE-mediated histamine releasability during immunotherapy.

Desensitization of IL-4 secretion from mouse bone marrow-derived mast cells

Several recent findings indicate that mouse bone marrow-derived mast cells (BMMC) express RNA encoding interleukin-4 (IL-4) and secrete detectable amounts of IL-4 in response to cross-linking of Fc epsilon RI receptors, Fc gamma R receptors, or to ionomycin. We investigated the desensitization of BMMC from the view point of both IL-4 secretion and histamine release. In a desensitization protocol, the cells were challenged with an optimal concentration of antigen (10 ng/ml of DNP33-BSA) in the absence of calcium for various periods of time followed by addition of calcium to determine the loss in ability to release histamine or IL-4. In the context of histamine release, BMMC were desensitized completely in 45 min (T1/2 approximately 5 min). By contrast, in the context of IL-4 secretion, BMMC were only partly desensitized (52 +/- 5% of the control response) after 1 h of desensitization. A longer-term (2-6 h) desensitization of BMMC did not result in complete inhibition of IL-4 secretion (44 +/- 5% of control after 6 h). Northern blot analysis showed that IL-4 mRNA accumulation was decreased after a 1 h desensitization (37% +/- 14% of non-desensitized cells), suggesting that desensitization of IL-4 release results from a decrease in the amount of mRNA accumulation. These and other data support the view that the IgE-mediated signal transduction cascade has meditor-specific pathways that are independently regulated by homeostatic mechanisms within mast cells.