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Serum and plasma stimulate prostaglandin production by alveolar macrophages
Abstract:
Fetal bovine serum (FBS) stimulated rabbit alveolar macrophages to synthesize prostaglandins (PG) and release lysosomal enzymes. This stimulatory action was not entirely due to the effect of foreign protein in FBS, since rabbit serum and plasma, both homologous and autologous, also induced release of PGs and lysosomal enzymes. Rabbit serum and plasma are less effective than FBS as a stimulus for PG release, with rabbit serum being more potent than plasma at the same concentration. Bovine serum albumin elicited a dose-dependent increase of arachidonic acid release by macrophages, but not of PG production. Hence, the fatty acid "trapping" effect of albumin in serum and plasma is not responsible for the PG stimulation. The PG stimulating factors were stable at 56 degrees C for 30 min., but lost half the activity after heating at 100 degrees C for 10 min. Gel permeation chromatography of FBS showed several peaks of PG stimulating and arachidonic acid releasing activity. The molecular weight of the major one (150,000 daltons) is similar to that of immunoglobulin G. Rabbit IgG, when added to the macrophage culture, stimulated release of arachidonic acid and PGs. However, the major stimulatory effect in serum or plasma is not all due to IgG, since removal of IgG by a Protein A-agarose column did not remove the stimulatory effect of FBS and rabbit serum. The possibility of other factors, such as complement fragments, is discussed.
Insights
Fetal bovine serum (FBS) and rabbit serum stimulate macrophages to release prostaglandins (PGs). These factors, potentially including immunoglobulin G and complement fragments, are not solely proteins, indicating complex immune signaling.
Area of Science:
- Immunology
- Cell Biology
Background:
- Fetal bovine serum (FBS) is known to stimulate macrophages.
- Macrophages play a key role in immune responses through prostaglandin (PG) synthesis and lysosomal enzyme release.
Purpose of the Study:
- To investigate the specific components in serum that stimulate prostaglandin (PG) synthesis and lysosomal enzyme release in rabbit alveolar macrophages.
- To determine if foreign proteins or other factors in serum are responsible for this stimulation.
Main Methods:
- Macrophages were cultured and stimulated with various serum preparations (FBS, rabbit serum, rabbit plasma) and purified components (bovine serum albumin, rabbit IgG).
- Prostaglandin production, lysosomal enzyme release, and arachidonic acid release were measured.
- Heat stability and molecular weight of stimulating factors were assessed using chromatography.
Main Results:
- Both FBS and rabbit serum/plasma stimulated PG and lysosomal enzyme release, with FBS being more potent.
- Bovine serum albumin increased arachidonic acid release but not PG production.
- Stimulatory factors were heat-stable to 56°C but partially inactivated at 100°C.
- A major stimulatory factor in FBS had a molecular weight of 150,000 daltons, similar to IgG.
- While rabbit IgG stimulated macrophages, its removal did not eliminate the stimulatory effect of serum, suggesting other factors are involved.
Conclusions:
- Serum components, beyond foreign proteins and albumin, significantly stimulate macrophage PG synthesis and enzyme release.
- Immunoglobulin G (IgG) contributes to, but is not solely responsible for, the observed stimulatory effects.
- Complement fragments or other uncharacterized factors may play a role in serum-mediated macrophage activation.