Monitoring eosinophils to guide therapy with Biologics in Asthma: does
the compartment matter?
The role of eosinophils in allergic inflammation is well recognized. In
homeostasis these cells are found in multiple healthy tissues including
the lung parenchyma, but the function of these resident eosinophils is
unknown. Circulating eosinophils are easily quantifiable and have been
used to define “eosinophilic phenotype”, and to select patients who
are likely to respond to anti-eosinophil and anti-Th2—directed
therapies. However, presence of eosinophils in circulation may not
necessarily indicate that the eosinophils are key effector cells for an
airway disease such as asthma and this may be reason for not all
patients responding well to anti-IL5 therapies despite normalization of
blood eosinophils. This pro-con commentary examines the role of
enumerating circulating vs luminal (sputum) eosinophils (and their
activation status) not only to initiate therapies with monoclonal
antibodies, but to monitor their clinical response while on therapy.