In infants, a transient low immunoglobulin G (IgG4) subclass level may cause recurrent wheezing and/or asthmatic symptoms, and may be a type of early transient wheezing, according to a study published in Pediatric Pulmonology. Muneaki Matsuo MD, PhD, and colleague evaluated 77 infants younger than 3 categorized into four groups (Group 1, controls; Group 2, infants with recurrent wheezing and multiple hospitalizations despite using inhaled corticosteroids [ICS]; Group 3, infants with recurrent wheezing without hospitalization after starting ICS; Group 4, allergic infants without wheezing). Among the four groups, serum IgG, IgM, IgA, IgG1, IgG2, and IgG3 levels did not differ considerably. However, the IgG4 level in Group 2 infants was much lower than in Groups 1, 3, and 4. “Of the 16 infants in Group 2, 10 were followed to age 6,” the study authors wrote. “Nine of them had no recurrent wheezing at age 6 without medication. In addition, their IgG4 levels at age 6 were significantly increased from those in infancy.”