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Human myeloma proteins of IgG₄ subclass in contrast to myeloma proteins IgG₁, IgG₂ and IgG₃, were capable of blocking PCA reactions in monkeys mediated by human reaginic antibodies of IgE class. In addition to IgE, IgG₄ myeloma protein was also capable of sensitizing leukocytes from normal individuals and gave histamine release (HR) upon challenge with anti-human IgG₄. Leukocytes from 11 allergic individuals and from 9 normal subjects sensitized with the serum of allergic patients, were capable of releasing histamine with anti-human IgG₄, anti-human IgE, and the specific allergen. No response was obtained with anti-human IgG₁ and IgG₃ sera. Leukocytes from the normal individuals released histamine from 3 to 20% with anti-human IgG₄ and from 6 to 30% with anti-human IgE. Moreover, normal leukocytes sensitized with IgG₄ myeloma protein or a serum of an allergic patient heated at 56°C for 2 h, released a significant amount of histamine on challenge with anti-human IgG₄ whereas no response was obtained with anti-human IgE. The biological role of human IgG₄ in immediate hypersensitivity reactions is discussed in relation to human IgE.

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One hundred and three patients (90 nonatopics and 13 atopics) with respiratory infections to various viral agents were studied retrospectively with respect to IgE immunoglobulin levels during acute (1 to 7 days) and convalescent (8 to 30 days) phases of infection. It was found that 59% of patients had a decrease of 20% or more in IgE level, 27% remained the same, and only 14% showed a rise 20% or more from the acute to the convalescent phases of infection. IgE levels decreased up to 3 to 4 wk after symptoms and the degree of decrease was more apparent for the nonatopics who had higher IgE levels in their acute phase of infection. Less dramatic decrease in IgE was observed for the 13 atopics studied. The changes in IgE levels during the viral infectious period are discussed in terms of possible cellular mechanisms that may control IgE immunoglobulin.

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12 of 93 patients with untreated seasonal ragweed rhinitis, strong skin sensitivity and 2 + to 4 + RAST gave insignificant (≤14%) histamine release from their leukocytes on challenge with ragweed allergen.

Comparison of intracutaneous skin tests and RAST in 2 groups of patients, one consisting of 16 individuals having multiple allergies to pollen, mold and animal dander and the other of 10 patients allergic to mold only, revealed that skin tests were more sensitive than RAST. Skin reactions of 3+ to 4+ were frequently associated with negative RAST results. This was observed more so in mold-allergic patients. In a few cases (6%) RAST showed 2+ reactions while the skin tests were negative. Leukocytes from allergic individuals who had positive skin tests and negative RAST released a significant amount of histamine upon challenge with specific allergen as well as antihuman IgG4, suggesting that this immunoglobulin is a functional component of some immediate hypersensitivity reactions.

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