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Development of functional diversity in mouse macrophages. Mutual exclusion of two phenotypic states
D J Laszlo1, P M Henson, L K Remigio
1Department of Pediatrics, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
Abstract:
The objective of this study was to investigate the mechanisms that contribute to the generation of macrophage functional diversity. Exposure of mouse bone marrow-derived macrophages to beta-1,3-glucan, a particulate inflammatory stimulus, or polyinosinate-polycytidylate (poly[I:C]), a stimulus of macrophage cytocidal activation, induced distinct and stimulus-specific patterns of gene expression. These changes were characterized by an up-regulation of the expression of the acid hydrolase beta-glucuronidase and platelet-derived growth factor B following incubation with beta-1,3-glucan and a stimulation of the expression of the complement component Bf, beta-interferon, and the reactive nitrogen intermediates NO2/NO3 during incubation with poly[I:C]. The induction of Bf expression by poly[I:C] could not be explained on the basis of distinct subpopulations of cells since in situ hybridization with a mouse Bf cRNA probe revealed a uniform and substantial increase in Bf expression by the entire population of cells. Incubation of macrophages with beta-1,3-glucan before stimulation with poly[I:C] was found to strongly attenuate the expression of Bf and beta-interferon. Conversely, incubation with poly[I:C] prior to exposure to beta-1,3-glucan substantially blocked the stimulation of beta-glucuronidase and platelet-derived growth factor B expression, indicating that these two responses were expressed in a mutually antagonistic fashion. However, after removal of either stimulus and following a period in which the primary response was allowed to decay, the cells regained their capacity to subsequently respond to either the same stimulus or to a different stimulus. Collectively, these findings indicate, first, that the heterogeneity of gene expression seen in response to poly[I:C] represents an adaptive response of the entire macrophage population rather than the restricted responses of distinct subpopulations of cells. Second, macrophages respond to these stimuli in a sequential fashion. These findings thus have a significant bearing on our understanding of the regulation of macrophage heterogeneity in host defense.
Insights
Macrophages exhibit functional diversity through stimulus-specific gene expression patterns. Pre-exposure to one stimulus antagonizes responses to another, but cells regain responsiveness over time.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Macrophage functional diversity is crucial for host defense.
- Understanding the mechanisms regulating macrophage heterogeneity is essential.
Purpose of the Study:
- To investigate the mechanisms generating macrophage functional diversity.
- To determine how distinct stimuli induce specific gene expression patterns in macrophages.
- To explore the sequential and antagonistic responses of macrophages to inflammatory stimuli.
Main Methods:
- Exposure of mouse bone marrow-derived macrophages to beta-1,3-glucan and polyinosinate-polycytidylate (poly[I:C]).
- Analysis of stimulus-specific gene expression patterns, including beta-glucuronidase, platelet-derived growth factor B, complement component Bf, and beta-interferon.
- In situ hybridization to assess the distribution of gene expression within the macrophage population.
- Sequential stimulation experiments to evaluate antagonistic and adaptive responses.
Main Results:
- Beta-1,3-glucan induced beta-glucuronidase and platelet-derived growth factor B expression.
- Poly[I:C] stimulated complement component Bf, beta-interferon, and reactive nitrogen intermediates (NO2/NO3).
- Pre-exposure to beta-1,3-glucan attenuated poly[I:C]-induced Bf and beta-interferon expression.
- Pre-exposure to poly[I:C] blocked beta-1,3-glucan-induced beta-glucuronidase and platelet-derived growth factor B expression.
- Macrophages regained responsiveness after stimulus removal, indicating sequential adaptation.
Conclusions:
- Macrophage heterogeneity in response to poly[I:C] is an adaptive response of the entire population, not distinct subpopulations.
- Macrophages respond to inflammatory stimuli in a sequential and mutually antagonistic manner.
- These findings enhance the understanding of macrophage heterogeneity regulation in host defense.