Differential Effects of Necrotic or Apoptotic Cell Uptake on Antigen Presentation by Macrophages

Abstract

The induction of pathogenic immune responses may be dependent on the immune system receiving ‘danger’ signals resulting from tissue damage, rather than tolerogenic stimuli associated with normal cell turnover. The aim was to test this hypothesis by comparing the effects of the uptake of necrotic and apoptotic cells on the ability of antigen-presenting cells (APC) to stimulate immune responses in vitro. The experiments focused on presentation by the macrophage, which is the main cell type adapted for clearing cellular debris in vivo. Murine bone marrow-derived macrophages were pulsed with neutrophils that had been rendered apoptotic or necrotic, and tested for the ability to induce T cell responses. The macrophages that had taken up necrotic, but not apoptotic, cells were able to stimulate recall proliferation by ovalbumin-specific T cells. Furthermore, the response to the mitogen concanavalin A (Con A) was more than 6 times higher when macrophages had been pulsed with necrotic, in comparison with apoptotic, cells. In control experiments, macrophages that had not been exposed to dying neutrophils stimulated weak responses to ovalbumin and Con A. To determine why the uptake of apoptotic and necrotic cells exert opposing effects on the ability of macrophages to stimulate T cells, the expression of costimulatory molecules by treated macrophages, and their production of potentially immunomodulatory cytokines were measured. Flow cytometry revealed that macrophages that had taken up necrotic, but not apoptotic, neutrophils expressed increased levels of CD40 compared to untreated controls within 4 h. Macrophages pulsed with apoptotic cells secreted higher levels of transforming growth factor-β1 than those ingesting necrotic cells or untreated controls. Our interpretation of these results is that macrophages that have taken up necrotic cell debris present antigens to T lymphocytes with greater efficiency due to transient CD40 upregulation, whereas those that have ingested apoptotic cells are ineffective APC since they secrete inhibitory cytokine.

Sepsis-Induced Apoptosis Causes Progressive Profound Depletion of B and CD4+ T Lymphocytes in Humans

“…Voll et al (24) demonstrated that addition of apoptotic lymphocytes to endotoxin-stimulated PBMC caused a shift from secretion of proinflammatory cytokines (TNF-␣, IL-1␤, and IL-12) to antiinflammatory cytokines (IL-10). Barker et al (25) showed that macrophages that ingested apoptotic cells had increased FIGURE 5. A, Comparison between septic and trauma for lymphoid follicles and total B cell area based on the duration of sepsis.…”

On the influence of neutrophils in corneas with necrotizing HSV-1 keratitis following amniotic membrane transplantation

“…Several reports have shown that such macrophages ingesting apoptotic cells not only fail to induce inflammation but also actively suppress an inflammatory immune response (Fadok et al, 1998(Fadok et al, , 2000. Macrophages with ingested apoptotic cells markedly decrease expression of CD40, a co-stimulatory factor for T-lymphocytes (Barker et al, 1999) of proinflammatory cytokines and increased production of prostaglandin E2 and transforming growth factor-b1 (Fadok et al, 1998), both factors involved as regulators of physiological T cell homeostasis, activation, differentiation, and effector function. Recently, it has been shown that cells of a macrophage cell-line cocultured with AM only underwent apoptosis when activated with IFN-γ, while apoptosis was not found when IFN-γ was absent (Li et al, 2006).…”

Osteopontin attenuation of dextran sulfate sodium-induced colitis in mice

“…43 One possibility in our colitis model is that exogenous OPN may contribute to the termination of inflammation by activating macrophages to take up apoptotic neutrophils, thereby leading to neutrophil clearance and the release of anti-inflammatory and reparative cytokines, such as TGF-b1. 44 Both in vitro and in vivo evidence suggest that secretion of TGF-b1 by macrophages can suppress pro-inflammatory signaling from Tolllike receptors, further stimulating tissue repair. 45,46 The attenuation of an inflammatory reaction coincides with the departure of macrophages through the lymphatics.…”