Platelet to leukocyte adherence phenomena associated with thrombocytopenia.

Two patients developed thrombocytopenia associated with an in vitro platelet to leukocyte adherence phenomenon (PLAP). In one patient, whole serum, intact plasma, and the IgG fraction of the serum could induce the PLAP of normal platelets in normal whole blood or buffy coat preparations. Passage of serum over a Sepharose column coupled with antihuman IgG resulted in the loss of all the PLAP activity. Activity could not be recovered from the whole serum or the IgG fraction of serum of the second patient; however, the PLAP was transferred to her newborn infant. In both patients, an unusual pulmonary illness accompanied the PLAP and thrombocytopenia.