Related Experiment Videos
Digestion and resynthesis of receptors binding IgG-sensitized erythrocytes on rat macrophages
Abstract:
The proteinase sensitivity of rat macrophage Fc receptors (FcR) binding rabbit IgG-sensitized sheep erythrocytes (EA) was analysed by incubating alveolar macrophages with trypsin, alpha-chymotrypsin, pronase, granulocytic elastase and inhibitors of protein biosynthesis. Even under conditions at which enzymes alone did not bring about any receptor degrading effect, a reduction of cycloheximide. After a temporary blockade of protein biosynthesis by cycloheximide of macrophages which had lost their FcR through treatment with pronase, a rapid reappearance of EA-binding activity could be observed when the cells were washed and incubated in medium without drug or enzyme. On the other hand, the blockade induced by actinomycin D could not easily be reversed. The rate of reappearance of EA-binding activity of alveolar macrophages (AM psi) was faster than that of peritoneal macrophages (PM psi). Our results may suggest an alternative explanation for the apparent resistance of receptors to proteolytic digestion. The finally observed result may be caused by re-expression of FcR--either newly synthesized or from an intracellular pool--as well as by an inaccessibility of the receptor to the enzyme.
Insights
Rat macrophage Fc receptors (FcR) binding activity reappeared rapidly after protease treatment, suggesting re-expression from intracellular pools or newly synthesized receptors, not just enzyme resistance.
Area of Science:
- Immunology
- Cell Biology
Background:
- Macrophage Fc receptors (FcR) mediate crucial immune functions, including antibody-dependent cellular cytotoxicity and phagocytosis.
- The sensitivity of FcR to proteolytic enzymes and the mechanisms of their regulation are not fully understood.
Purpose of the Study:
- To investigate the proteinase sensitivity of rat macrophage Fc receptors (FcR) that bind rabbit IgG-sensitized sheep erythrocytes (EA).
- To explore the role of protein biosynthesis in the recovery of FcR-mediated binding activity after enzymatic treatment.
Main Methods:
- Alveolar and peritoneal macrophages were incubated with various proteinases (trypsin, alpha-chymotrypsin, pronase, granulocytic elastase).
- Protein biosynthesis was inhibited using cycloheximide and actinomycin D.
- Reappearance of EA-binding activity was monitored after enzyme treatment and subsequent incubation with or without inhibitors.
Main Results:
- Enzymes alone did not cause significant FcR degradation, but cycloheximide treatment reduced EA-binding activity.
- Following pronase treatment and cycloheximide blockade, EA-binding activity rapidly reappeared upon removal of the drug and enzyme.
- Actinomycin D-induced blockade was less reversible.
- The rate of reappearance was faster in alveolar macrophages (AM psi) compared to peritoneal macrophages (PM psi).
Conclusions:
- The apparent resistance of FcR to proteolytic digestion may be due to re-expression of receptors from intracellular stores or de novo synthesis.
- Differences in reappearance rates between alveolar and peritoneal macrophages suggest distinct regulatory mechanisms.
- FcR regulation involves dynamic processes of synthesis and potential intracellular compartmentalization.