Immunology of Apoptosis and Necrosis

Cortical expression of IL1-β, Bcl-2, Caspase-3 and 9, SEMA-3a, NT-3 and P-glycoprotein as biological markers of intrinsic severity in drug-resistant temporal lobe epilepsy

Mesial temporal lobe epilepsy (mTLE) is the most common epilepsy induced by previous cerebral injury, and one out of three mTLE patients develops drug resistance (DR).

AIM

To assess the expression of Bcl-2, Caspase-3, Caspase-9, IL1-β, SEMA-3a, NT-3 and P-glycoprotein in the temporal cortex and their relationship with the progression of mTLE-DR clinical features in patients with mTLE-DR.

METHOD

Tissue samples from 17 patients were evaluated for protein expression by Western blot and the relationships of the evaluated proteins with the clinical features of the mTLE were assessed through hierarchical cluster analysis.

RESULTS

The mTLE-DR group showed significantly higher P-glycoprotein, Bcl-2 and Caspase-9 levels ***p < 0.0001, ****p < 0.0001 and ***p < 0.0002, respectively, than the autopsy control group. Four patient clusters were identified: Clusters 1 and 3 showed relationships among the age of mTLE onset, duration of mTLE-DR, average number of epileptic seizures per week, number of previous antiepileptic drugs (AEDs) and increased expression of Caspase-3, Caspase-9, Neurotrophin-3 and Semaphorin-3a. Clusters 2 and 4 showed relationships among the mTLE onset age, current age, average number of epileptic seizures per week, number of previous AEDs and increased expression of IL1-β, Bcl-2, P-glycoprotein, Caspase-3 and NT-3.

CONCLUSION

The relationships among the clinical data the age of mTLE onset, DR duration, number of previous AEDs, and average number of seizures per week and the expression of proteins involved in neuronal death, neuroinflammation and aberrant connection formation, as which are biological markers in the cerebral temporal cortex, are important factors in the progression and severity of mTLE-DR and support the intrinsic severity hypothesis.

Ex vivo- and in vivo-induced dead tumor cells as modulators of antitumor responses

Joint application of standard tumor therapies like radiotherapy and/or chemotherapy with immune therapy has long been considered not to fit. However, it has become accepted that immune responses may contribute to the elimination of cancer cells. We present how in vivo-induced tumor cell death by irradiation, chemotherapeutic agents, or hyperthermia can be rendered more immunogenic. High hydrostatic pressure is introduced as an innovative inactivation method for tumor cells used as vaccines. Annexin A5, being a natural occurring ligand for phosphatidylserine that is exposed by dying tumor cells, renders apoptotic tumor cells immunogenic and induces tumor regression. Combinations of irradiation with hyperthermia may also foster antitumor responses. For preparation of autologous tumor cell vaccines, high hydrostatic pressure is suitable to induce immunogenic cancer cell death. Future work will be aimed toward evaluating which combination and chronological sequence of radiotherapy, chemotherapy, hyperthermia, annexin A5, and/or autologous tumor cell vaccines will induce specific and long-lasting antitumor immunity.

The immune reaction against allogeneic necrotic cells is reduced in Annexin A5 knock out mice whose macrophages display an anti-inflammatory phenotype

Proteins of the annexin family bind to phospholipids in a Ca²⁺ dependent manner. The exposure of phosphatidylserine (PS) by apoptotic as well as necrotic cells is one major eat-me-signal for macrophages. Annexin A5 (Anx A5) preferentially binds to PS. The availability of Anx A5 knock out (KO) mice allowed us to investigate for the first time if endogenous Anx A5 modulates the immune response towards allogeneic cells. Furthermore, the effect of Anx A5 gene deletion on the phagocytic process as well as on the inflammatory reaction of macrophages was explored. We found that Anx A5 KO mice have a strongly reduced allogeneic cellular immune reaction against primary as well as secondary necrotic cells. In vivo phagocytosis experiments revealed that macrophages of Anx A5 KO mice displayed an increased uptake of necrotic cells. Additionally, an increased secretion of the anti-inflammatory cytokine IL-10 of isolated macrophages of Anx A5 KO mice after contact with necrotic cells was observed. Furthermore, the promoter activity of the Anx A5 gene was enhanced after stimulation of macrophages. The tumour size of an allogeneic tumour regressed faster when endogenous Anx A5 was present. These data demonstrate that endogenous Anx A5 influences the phagocytosis of necrotic cells, modulates the immune response towards allogeneic cells and acts as an inflammatory protein.

Apoptosis-associated antigens recognized by autoantibodies in patients with the autoimmune liver disease primary biliary cirrhosis

There is growing evidence that the onset of autoimmune disorders can be linked to the inefficient removal of apoptotic cells. Since defects in the elimination of apoptotic cells lead to secondary necrosis and subsequent release of intracellular components, this might explain the generation of autoantibodies against intracellular antigens. Accordingly, we wanted to investigate, whether antibodies from patients with the autoimmune liver disease primary biliary cirrhosis (PBC) recognize self-proteins generated and released during apoptosis. Using Western blot analyses we could detect intracellular antigens with serum IgG from PBC patients but not with serum IgG from healthy donors in lysates of Jurkat T-leukemia, HepG2 hepatoma, and HT-29 colon-carcinoma cells. Interestingly, PBC serum IgG also recognized caspase substrates in cells undergoing apoptosis induced by staurosporine or TRAIL (TNF-related apoptosis inducing ligand). In addition to intracellular antigens, serum IgG from PBC patients detected caspase-dependent antigens in the supernatants of apoptotic (secondary necrotic) cells and antigens on the surface of apoptotic Jurkat cells. Among the caspase substrates recognized by PBC serum IgG we could identify the components PDC-E2 and -E1beta of the known autoantigen PDC (pyruvate dehydrogenase complex). Thus, caspase-mediated processing of intracellular proteins might generate de novo autoantigens that upon release contribute to the generation of autoantibodies and autoimmune diseases as PBC.

Vaccination against prostate cancer using a live tissue factor deficient cell line in Lobund-Wistar rats

Reducing expression of the tissue factor gene in prostate adenocarcinoma cells (PAIII) results in a cell line that, in vivo, mimics the growth of wildtype (wt) PAIII. However, instead of continuing to grow and metastasize as wt PAIII tumors do, tissue factor deficient PAIII (TFD PAIII) masses spontaneously regress after several weeks. Although whole cell vaccines are typically inactivated prior to administration to prevent proliferation within the host, numerous studies have suggested that exposure to live, attenuated, whole tumor cells, and the extracellular microenvironment they recruit, increases immunotherapeutic potential. Here, we provide support for this notion, and a strategy through which to implement it, by demonstrating that subcutaneous vaccinations with the TFD PAIII protect the Lobund-Wistar rat against subsequent wt PAIII cell challenge. TFD PAIII immunized rats suffered significantly less metastasis of wt PAIII challenge tumors compared to unvaccinated naïve controls rats. These results offer the intriguing possibility that the TFD PAIII vaccine is an effective system for the prevention and, possibly, the treatment of prostate cancer.

The influence on the immunomodulatory effects of dying and dead cells of Annexin V

Apoptotic and necrotic cells expose phosphatidylserine (PS). This membrane modification ensures a swift recognition and uptake by phagocytes of the dying and dead cells. Annexin V (AxV) preferentially binds to anionic phospholipids and thereby, modulates the clearance process. First, we analyzed the influence of AxV on the immunogenicity of apoptotic cells. The addition to apoptotic cells of AxV prior to their injection into mice increased their immunogenicity significantly. Next, we studied the influence of endogenous AxV on the allogeneic reaction against apoptotic and necrotic cells. To preserve heat-labile, short-lived "danger signals," we induced necrosis by mechanical stress. Wild-type mice showed a strong, allogeneic delayed-type hypersensitivity (DTH) reaction. In contrast, AxV-deficient animals showed almost no allogeneic DTH reaction, indicating that endogenous AxV increases the immune response against dead cells. Furthermore, AxV-deficient macrophages had a higher immunosuppressive potential in vitro. Next, we analyzed the influence of AxV on chronic macrophage infection with HIV-1, known to expose PS on its surface. The infectivity in human macrophages of HIV-1 was reduced significantly in the presence of AxV. Finally, we show that AxV also blocked the in vitro uptake by macrophages of primary necrotic cells. Similar to apoptotic cells, necrotic cells generated by heat treatment displayed an anti-inflammatory activity. In contrast, mechanical stress-induced necrotic cells led to a decreased secretion of IL-10, indicating a more inflammatory potential. From the experiments presented above, we conclude that AxV influences the clearance of several PS-exposing particles such as viruses, dying, and dead cells.