Early-life respiratory tract infections by rhinovirus (RV) are considered risk factors for asthma development. Previous studies have shown that RV infection of six-day-old BALB/c mice, but not mature mice, induces an asthma-like phenotype, including mucous metaplasia and airway hyperresponsiveness, which is associated with the expansion of type 2 innate lymphoid cells (ILC2s). This chapter describes the isolation and analysis of ILC2s from RV-infected neonatal mouse lungs by flow cytometry, in vitro culture and adoptive transfer.