Autoimmunity in MFG-E8–deficient mice is associated with altered trafficking and enhanced cross-presentation of apoptotic cell antigens
YuFeng Peng, Keith B. Elkon
YuFeng Peng, Keith B. Elkon
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Research Article Autoimmunity

Autoimmunity in MFG-E8–deficient mice is associated with altered trafficking and enhanced cross-presentation of apoptotic cell antigens

Abstract

Apoptotic cells must be rapidly cleared, as defects in this process can lead to autoimmunity. Milk fat globule EGF factor 8 (MFG-E8) binds to apoptotic cells and facilitates their removal through interaction with phagocytes. Mice deficient in MFG-E8 develop lupus-like autoimmunity associated with accumulation of apoptotic cells in vivo. Here, we have shown that MFG-E8 controls phagocytic ingestion of cell fragments as well as their intracellular processing into MHC-antigen complexes. Older Mfge8–/– mice spontaneously developed dermatitis associated with CD8+ T cell infiltration and striking activation of effector memory CD8+ T cells. CD8+ T cell responses to both exogenous and endogenous apoptotic cell–associated antigens were enhanced in Mfge8–/– mice. MFG-E8 deficiency accelerated the onset of disease in a mouse model of autoimmune diabetes. Enhanced CD8+ T cell responses were attributed to increased cross-presentation by DCs along with increased detection of antigen-MHCI complexes. Intracellular trafficking analysis revealed that intact apoptotic cells ingested by wild-type DCs rapidly fused with lysosomes, whereas smaller fragments persisted in Mfge8–/– DC endosomal compartments for 24 hours. These observations suggest that MFG-E8 deficiency promotes immune responses to self antigens not only by delaying the clearance of dying cells but also by altering intracellular processing, leading to enhanced self-antigen presentation.

Authors

YuFeng Peng, Keith B. Elkon

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Figure 15

Recombinant MFG-E8 reverses enhanced cross-presentation by Mfge8–/– BMDCs.

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Recombinant MFG-E8 reverses enhanced cross-presentation by Mfge8–/– BMDC...
(A) Day-6 BMDCs from either WT or Mfge8–/– mice were incubated with Apo-OVA for 24–36 hours. Recombinant MFG-E8 was mixed with apoptotic cells before adding to Mfge8–/– BMDCs at a final concentration of 0.2 μg/ml. Apo-OVA–containing BMDCs were collected to stimulate CFSE–labeled OT-I CD8+ T cells with total DC/T ratios of 1:1 and 3:1. OT-I T cell proliferation and CD62L downregulation were analyzed by flow cytometry at day 3. The results from 2 out of 3 independent experiments are shown. Right: division indices from 3 independent experiments **P = 0.05, *P = 0.08, ****P = 0.025, ***P = 0.04, paired t test. (B) As controls, BMDCs were incubated with either OVA peptide (10 μM) for 1 hour or with soluble OVA protein (200 μg/ml) overnight. After washing with medium, DCs were used to stimulate OT-I T cells (red, Mfge8–/– BMDCs; green, Mfge8–/– BMDCs plus rMFG-E8; blue, WT BMDCs). Both control experiments were performed twice with similar results.