The novel human IgE epsilon heavy chain, epsilon tailpiece, is present in plasma as part of a covalent complex.

Several splice variants of the secreted human epsilon heavy chain have previously been identified by reverse transcription-PCR. The heavy chain of one isoform, IgE tailpiece, differs from the originally identified IgE, IgE classic, by the replacement of the 2 carboxy-terminal amino acids by 8 novel amino acids including a carboxy-terminal cysteine residue. Recombinant human epsilon tailpiece and epsilon classic heavy chains were expressed and secreted as H2L2 monomers in Sp2/0 murine myeloma cells. We have investigated the in vitro function and in vivo occurrence of epsilon tailpiece heavy chains using receptor binding assays, granule release assays, flow cytometry, half-life studies, immunoprecipitation, SDS-PAGE, two-dimensional SDS-PAGE, and Western blotting. IgE tailpiece and IgE classic exhibited similar in vivo half-lives in BALB/c mice, bound the human high- and low-affinity IgE receptors with similar affinities and triggered equivalent levels of high affinity IgE receptor induced degranulation. In humans, IgE classic is present as a 190 kD circulating protein in vivo. In contrast, we found that in plasma epsilon tailpiece was primarily present as part of covalent complexes of approximately 300 and 338 kD. Dissociation of the complexes revealed that two species of epsilon tailpiece heavy chains were present therein and surprisingly, these in vivo derived epsilon tailpiece heavy chains were approximately 5 and 10 kD smaller than the recombinant expressed epsilon tailpiece or epsilon classic heavy chains. These results show that epsilon tailpiece is present in novel covalent complexes in humans.

Ineffectiveness of continuous quinidine gluconate infusion in the treatment of severe chloroquine-resistant Plasmodium falciparum malaria.

The drug of choice in the treatment of chloroquine-resistant Plasmodium falciparum malaria is parenteral quinine dihydrochloride. Due to limited use, the drug is not commercially available in the U.S. and must be obtained through the Centers for Disease Control (CDC) in Atlanta, Georgia. As an alternative, the CDC has developed a protocol to treat P. falciparum malaria with parenteral quinidine gluconate. Following this protocol, a 10 mg/kg loading dose of quinidine gluconate followed by a 0.02 mg/kg/min continuous infusion was administered to a 53-year-old man with severe life-threatening chloroquine-resistant P. falciparum malaria. Although the patient described did not survive, the use of parenteral quinidine gluconate still appears to be a viable alternative to parenteral quinine dihydrochloride in the treatment of severe chloroquine-resistant P. falciparum malaria.