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The allergen Dpt 4 from the house dust mite Dermatophagoides pteronyssinus was shown to be a lipoprotein as judged by its Sudan black B staining properties. Ultracentrifugal studies confirmed this finding and showed that Dpt 4 was polydisperse, although the majority of the allergen belonged to a very high density lipoprotein class. Physicochemical studies using gradient polyacrylamide gel electrophoresis showed that Dpt 4 had an apparent molecular weight of 244,000 daltons and a particle diameter of 10.73 nm. Agarose gel electrophoresis showed that the allergen had an electrophoretic mobility 0.86 times that of human alpha-lipoprotein. The observation that Dpt 4 is a lipoprotein is consistent with earlier studies which showed that the allergen was heterogeneous with regard to its molecular weight and that it contained the hapten phosphorylcholine.

Components with hapten-like properties were isolated from the nondialyzable fraction, i.e. the retentate (R) and the dialyzable fractions of the aqueous extract of Kentucky Blue Grass pollen (KBC aq.ext.), by preparative isoelectrofocussing on Sephadex G-100 gel. These haptenic components could not elicit the passive cutaneous anaphylaxis (PCA) reactions in rats passively sensitized with a murine reaginic antiserum to R, but could inhibit completely and specifically the PCA reaction which is normally elicitable with R. It was concluded that the specificity of the murine IgE antibodies was directed to a determinant(s) which was common to either allergenic or haptenic fractions. Moreover, by employing a pool of human sera from individuals allergic to KBG pollen in the radioallergosorbent test procedure, it was apparent that most of the haptenic fractions lacked some of the specificities present on allergenic components of R that were recognized by the human IgE antibodies. Evidence was obtained to suggest that the electrophoretic heterogeneity of allergenic components present in various fractions of KBG aq.ext. may be due primarily to differences in their net charge, rather than to differences in their allergenic specificity.