Biomedical subjects

D F Singer

Publications and source records attributed to D F Singer.

3 recordsLinked to original sources

PubMed1995

Antigen-presenting cell lines internalize peptide antigens via fluid-phase endocytosis.

In this report, we present experimental evidence that antigen-presenting cell lines take up peptide antigens in a manner consistent with fluid-phase endocytosis. Using the fluid phase endocytic marker inulin and a mathematical model for fluid phase uptake, we have found a basal uptake rate constant of approximately 0.9-2 microns 3/cell minutes in A20, TA3, and J774 cells. An influenza virus peptide, PB2(303-313), the octapeptide, angiotensin II, an ovalbumin peptide, OVA(323-339), and a guinea pig myelin basic protein peptide, MBP(72-86), have uptake rate constants comparable to inulin, i.e., between 1 and 4 microns3/cell minutes in A20 cells. However, another influenza virus peptide, PB2(146-159), has an uptake rate constant approximately sixfold higher than that found for inulin in A20 cells. We have also determined that the peptide antigens we tested are retained in A20 cells similarly to inulin, with half-times calculated to be from 2 to 13 min as compared to 2 min for inulin. Notably, these results were obtained over short incubation times (up to 20 min) and under conditions that restrict peptide proteolysis and also protein synthesis. We conclude from these studies that peptide antigens enter antigen-presenting cells via fluid-phase endocytosis.

Animals↗

PubMed1991

Antigen processing and presentation: how can a foreign antigen be recognized in a sea of self proteins?

A mathematical model describing the time-dependent events of antigen processing and presentation is utilized to quantitatively analyze the importance of newly synthesized Ia molecules as well as Ia molecules internalized from the cell surface in the formation of Ia-antigen complexes, the T cell receptor ligand. It has recently been shown that antigen presenting cells are not selective for the proteins they process and present. Therefore, we also investigate the ability of macrophages and B cells to process and present antigen in the presence of competing proteins often present in the extracellular environment. A set of criteria is formulated based upon experimental data to determine the validity of two model variations. We draw two major conclusions from our simulations. First, we determine that macrophages and B cells can present between 1-3 Ia-antigen complexes micron-2 for antigen concentrations in the range of 4-7 microM while in the presence of approximately 0-10 microM competing proteins or peptides. Second, we find it likely that antigen presenting cells, both B cells and macrophages, need to internalize Ia molecules from the cell surface in order for a sufficient number of Ia-antigen complexes to be presented. Binding of antigen to newly synthesized Ia alone does not, given experimentally reported values for Ia synthesis, allow sufficient Ia-antigen complex formation.

B-Lymphocytes↗

PubMed1990

The relationship between antigen concentration, antigen internalization, and antigenic complexes: modeling insights into antigen processing and presentation.

Native antigen is processed and subsequently presented on the surface of antigen-presenting cells, an important step in the elicitation of an immune response. The early events of antigen processing and presentation include: ingestion of a native antigen, intracellular degradation to expose an antigenic peptide fragment, binding of this fragment with an MHC class II molecule, and display of this newly formed complex on the cell surface. Through the development of a mathematical model, a set of mathematical equations which describes the time-dependent appearance, disappearance, and movement of individual molecules, quantitative insight can be gained into the pathways and rate-limiting steps of antigen presentation. The credibility of the model has been verified by comparison to literature data. For example, it has been shown experimentally that macrophages require 60 min for effective antigen presentation, whereas B cells require 6-8 h. The mathematical model predicts these presentation times and identifies the difference in the cell's respective pinocytic rates and sizes as important parameters. B cells capture antigen in their environment through nonspecific fluid-phase pinocytosis as well as by binding antigen to their surface immunoglobulin, allowing receptor-mediated uptake. Uptake of antigen via receptor-mediated endocytosis has been reported to require 1,000-fold less antigen than uptake via nonspecific pinocytosis. The mathematical model clearly predicts this decrease in concentration. The model also makes quantitative predictions for the number of MHC class II-antigen complexes needed to produce T cell stimulation.

Animals↗