title: Characterization of bilirubin transport system by human peripheral blood mononuclear cells.
abstract: Decreased immune responses have been observed in hyperbilirubinemic patients. This study investigates bilirubin transport into human peripheral blood mononuclear cells (PBMNCs). In vitro incubation of PBMNCs at 37 degrees C with 0-12 mg/dl bilirubin in solution with a fixed bovine serum albumin (BSA) concentration (3.0 g/dl) resulted in a dose-dependent increase of intracellular bilirubin in both monocytes and lymphocytes. Bilirubin uptake in monocytes was significantly higher (up to 2.7 times) than in lymphocytes under the same culture conditions. When PBMNCs were incubated with varying concentrations of bilirubin (0-16 mg/dl) in fixed BSA (3.0 g/dl) solution or at a fixed bilirubin/albumin molar ratio (0.4), the initial velocity of uptake in both cell fractions was proportional to the free (unbound to albumin) bilirubin concentration rather than the total bilirubin concentration. Bilirubin uptake by both cell fractions was significantly inhibited by treatment with metabolic inhibitors. Bilirubin uptake by monocytes continued to increase in parallel with incubation temperature from 0 degrees C to 40 degrees C, whereas uptake by lymphocytes reached a maximal level at 20 degrees C and remained constant thereafter. These results suggest that monocytes and lymphocytes incorporate bilirubin in proportion to the free bilirubin concentration and this function may rely on different energy-dependent mechanisms.
authors.affiliation: Department of Internal Medicine, University of Nebraska Medical Center, Omaha 68198.
authors.forename: Y
authors.initials: Y
authors.lastname: Haga
authors.forename: M A
authors.initials: MA
authors.lastname: Tempero
authors.forename: H D
authors.initials: HD
authors.lastname: Kay
authors.forename: R K
authors.initials: RK
authors.lastname: Zetterman
mesh_terms: D000328:Adult; D001386:Azides / Q000494:pharmacology; D001663:Bilirubin / Q000493:pharmacokinetics*; D001692:Biological Transport / Q000502:physiology; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004734:Energy Metabolism / Q000187:drug effects / Q000502:physiology; D005434:Flow Cytometry; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D008875:Middle Aged; D009840:Oligomycins / Q000494:pharmacology; D019810:Sodium Azide; D013696:Temperature; D013997:Time Factors
chemical_list: D001386:Azides; D009840:Oligomycins; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D019810:Sodium Azide; D001663:Bilirubin