Factors That Determine LAR
Several factors are probably important in determining whether an allergic reaction subsides after an immediate response or progresses to a late phase reaction. One modulating factor is the level of antigen-specific IgE within the host; higher levels of IgE have generally correlated with the development of LARs. Conversely, antigen-specific IgG may protect against these reactions. Information supporting this view is found in the rabbit model of the LAR- and in the skin of man. The level of airway reactivity also appears to be important: asthmatic patients with more reactive airways are more likely to develop late phase responses. Gonzales and associates found that, in atopic asthmatic patients with only an immediate asthmatic response, there was a significant increase in the percentage and absolute number of T-suppressor cells (OKT8) in bronchoalveolar lavage fluid, raising the possibility that mobilization of T-suppressor cells into the lung prevents a subsequent late phase reaction. cipro antibiotic
In addition, studies from Johns Hopkins University have suggested that histamine-releasing factors, factors derived from mononuclear cells and other sources and which may be found in late phase reactions in vivo, release histamine by binding and presumably cross-linking appropriate types of IgE.® Finally, observations in a canine model of LAR suggest that endogenous glucocorticosteroids may also determine if LAR will occur. Sasaki et al demonstrated dual responses when naturally allergic dogs were treated one hour before and two hours after Ascaris challenge with metyrapone, a cortisol synthesis inhibitor. Ascaris-sensitive dogs not treated with metyrapone had immediate, but no late, asthmatic responses. By inhibiting endogenous glucocorticosteroid synthesis, the investigators demonstrated both the physiologic changes of LAR and a neutrophil-rich inflammatory reaction within the airways, as assessed by lavage and histology.
Tags: airway, Asthma, phase reactions