Understanding CNS niche occupancy by microglia and macrophages in health and disease:
In the first of two studies led by PhD student Harald Lund we developed a novel model of microglia depletion using diptheria toxin expressed under the CX3CR1 receptor, which is highly expressed by microglia. The CNS did not allow the permanent depletion of its myeloid cells, and thus blood-circulating monocytes were accepted into the empty niche and adapted to the new environment. The characterization of this process was described in the first Nature Communications paper. We then depleted TGFbeta receptor signaling on the infiltrating monocytes, and this led to development of a novel neurodegenerative disease state that we characterised in the second Nature Immunology paper.
Lund H, Pieber M, Parsa R, Han J, Grommisch D, Ewing E, Kular L, Needhamsen M, Butovsky O, Jagodic M, Zhang X-M, Harris RA: Competitive repopulation of an empty microglial niche gives rise to functionally distinct subsets of microglia-like cells. Nature Communications 2018 9:4845
Lund H, Pieber M, Parsa R, Grommisch D, Ewing E, Kular L, Han J, Zhu K, Nijsen J, Hedlund E, Needhamsen M, Ruhrmann S, Ortlieb Guerreiro Cacais A, Berglund R, Forteza MJ, Ketelhuth DFJ, Butovsky O, Jagodic M, Zhang X-M, Harris RA: Fatal demyelinating disease is induced by monocyte-derived macrophages in the absence of TGF-β signaling. Nature Immunology 2018;19:1-7
The consequences of post-translational modifications for autoantigens:
In the first of these 3 studies led by PhD student Andreas Warnecke he devised, wrote a script for and further developed a programme for visualising the 3-d form of post-translationally modified proteins using known structures, a resource which is openly available online.
Warnecke A, Sandalova T, Achour A, Harris RA: PyTMs: A useful PyMOL plugin for modeling common post-translational modifications. BMC Bioinformatics 2014;15:370
In subsequent studies Andreas determined that the functional consequences of PTM modification of autioantigens determined the molecular interactions with myeloid cells, and that the immunological outcome was MHC-dependent:
Warnecke A, Musunuri S, N'diaye M, Sandalova T, Achour A, Bergquist J, Harris RA: Nitration of MOG diminishes its encephalitogenicity depending on MHC haplotype. Journal of Neuroimmunology 2017;303:1-12
Warnecke A, Abele S, Musunuri S, Bergquist J, Harris RA: Scavenger Receptor A mediates the clearance and immunological screening of MDA-modified antigen by M2 type macrophages. NeuroMolecular Medicine 2017;9:463-479
Immunosuppressive macrophage cell therapy modulates development of autoimmune disease
In a series of studies we developed a robust protocol for induction of potently immunosuppressive macrophages that for the fundament to our concept of myeloid cell therapy.
In the fiorst of these studies PhD student Roham Parsa demonstrated a significant prevention of development of Type 1 diabetes following macrophage cell therapy. The effect was even more dramatic considering that the therapy was initiated directly before disease onset, a timepoint proven difficult to immunomodulate in most other therapy studies in the NOD Type 1 Diabetes model:
Parsa R, Andresen P, Gillett A, Mia S, Zhang X-M, Mayans S, Holmberg D, Harris RA: Adoptive Transfer of Immunomodulatory M2 Macrophages Prevents Type 1 Diabetes in NOD Mice. Diabetes 2012;61:2881-92
Postdoc Xingmei Zhang conducted a similar study in a model of neuroinflammation, and likewise could demonstrate a significant reduction in development of paralytic disease, even when the therapy was initiated during the chrinic disease phase, a timepoint again difficult to modulate in previous attempts by other research groups:
Zhang X-M, Lund H, Mia S, Parsa R & Harris RA: Adoptive transfer of cytokine-induced immunomodulatory adult microglia attenuates experimental autoimmune encephalomyelitis in DBA/1 mice. Glia 2014;62:5 804-817
Importantly, PhD student Sohel Mia could then use the same stimulation protocol to prove that human macrophages from autoimmune patients were efficient at inhibiting their own pathogenic T cells in in vitro assays, providing a translational proof-of-concept.
Mia, S, Warnecke A, Zhang X-M, Harris RA: An optimized protocol for human M2 macrophages using M-CSF and IL-4/IL-10/TGF-β yields a dominant immunosuppressive phenotype. Scandanavian Journal Immunology 2014;79:305-14
One of the hallmark cytokines produced by the immunosuppressive macrophages is TGFβ, and the importance of this cytokine in maintaining cellular homeostasis was exemplified in PhD student Roham Parsa's study which revealed a worsening of neuroinflammation in the absence of TGFβ signaling:
Parsa R, Lund H, Tosevski I, Zhang XM, Malipiero U, Beckervordersandforth J, Merkler D, Prinz M, Gyllenberg A, James T, Warnecke A, Hillert J, Alfredsson L, Kockum I, Olsson T, Fontana A, Suter T, Harris RA: TGFβ regulates persistent neuroinflammation by controlling Th1 polarization and ROS production via monocyte-derived dendritic cells. Glia 2016;64:1925-37
A novel principle for improved humoral vaccination
In this study PhD student Roham Parsa set out to generate a macrophage-deficient mouse strain, but instead developed a neutrophil-deficient mouse strain. Through characterising the respective roles of neutrophils in early and late phases of immune activation, we could conclude that manipulation of neutrophil numbers at the site of inoculation would be a means of generating enhanced antibody responses to the injected substance:
Parsa R, Lund L, Georgoudaki A-M, Zhang X-M, Ortlieb Guerreiro-Cacais A, Grommisch D, Warnecke A, Croxford AL, Jagodic M, Becher B, Karlsson MCI, Harris RA: BAFF-secreting neutrophils drive plasma cell genesis during emergency granulopoiesis. Journal of Experimental Medicine 2016;213:1537-53