Phagocyte Biology Laboratory

Dr. Bryan Heit, Western University

About Us

Welcome! You have reached the homepage for the laboratory of Dr. Bryan Heit. Our lab is part of the Department of Microbiology and Immunology at Western University, and we are members of the Center for Human Immunology, the lead centre for the CIHR Human Immunology Network.

Our interests surround the function of phagocytes – white blood cells which ingest (phagocytose) pathogens, particles, and dead cells. We focus on the cellular and molecular processes which control the function of these cells during the maintenance of homeostasis, infection and chronic inflammatory disease. Central to most of our studies is the study of efferoctyosis – the phagocytic removal of apoptotic (dying) cells, and how failures in this process lead to inflammation, autoimmunity and infection.

What is a Phagocyte?

Phagocytes are a class of white blood cells which have the capacity to engulf large particles such as bacterial and fungal pathogens, and subsequently destroy the engulfed material. The term phagocyte literally translates to “cell that eats”, which is an apt description of the primary function of these cells in our bodies. While there are many types of phagocytes, the Heit lab focuses primarily on macrophages, which play key roles in both maintaining our bodies and in fighting infections.

Lab News

HIV Immunevasion

HIV We are excited to announce the publication of a collaborative study, investigating one mechanism which is used by HIV to evade the immune system. This study, a product of our long-standing collaboration with Jimmy Dikeako’s lab at Western University, discovered that the HIV protein Nef sequesters a key component of the immune system (MHC I) inside the cell. MHC I normally acts to present small fragments of pathogens such as HIV to immune cells, thereby allowing the immune system to identify and remove infected cells. By sequestering MHC I inside of infected cells, HIV “blinds” the immune system to its presence, allowing its infection to go unchecked.

This study builds upon the two previous collaborative studies produced by the Heit and Dikeakos lab – our initial description of the interaction between Nef and host cell proteins, and our development of new analysis methods for super-resolution microscopy.

Dirk BS, Pawlak EN, Johnson AL, Van Nynatten LR, Jacob RA, Heit B, Dikeakos JD. HIV-1 Nef sequesters MHC-I intracellularly by targeting early stages of endocytosis and recycling. Scientific Reports. 2016 Nov 14;6:37021. [Pubmed] [Article]

Efferocytosis Assays

quantitative efferocytosis assaysThe Heit lab is excited to announce our latest publication titled Quantitative Efferocytosis Assays, and published in Methods in Molecular Biology [Pubmed] [Article]. This paper describes many of the microscopy and cell based methods we use to study efferocytosis – the processes by which cells such as macrophages identify, engage, engulf and destroy dying (apoptotic) cells.

Efferocytosis plays a key role in maintaining homeostasis. The normal turnover of cells produces tens of billions of dying cells every day which must be removed. During times of injury or infection, the numbers of dying cells generated in our body can reach astronomical proportions, with some studies estimating that as many as 100 billion dying cells are produced daily during these events. Defects in efferocytosis leads to a range of clinical conditions including inflammatory diseases such as atherosclerosis, and autoimmune diseases such as multiple sclerosis. The clinical burden and cost of these diseases is immense, as is the human toll they impart, and as a consequence, understanding efferocytosis is paramount for reducing the burden of these diseases.

A range of methods can be found in this paper, including techniques to prepare and label synthetic targets which mimic dying cells, techniques to prepare and label dying cells such that they are compatible with a range of assays, and techniques to quantify the efferocytic efficiency, and methods to assess the processing of these efferocytic targets, all using a variety of microscopy techniques.

Many of these methods are derived from classical assays for quantifying phagocytosis, the removal and destruction of pathogens by immune cells. Because of this classical basis, many of these methods can be easily employed in most labs without the need for advanced cell processing or microscopy equipment. However, these methods can be combined with advanced live-cell fluorescence microscopy and even super-resolution microscopy, enabling their use in experiments reliant on leading-edge technologies. The methods described in this paper are applicable to a broad range of research questions and investigative approaches, and can be deployed in most labs.

Reference:

Evans AL, Blackburn JW, Yin C, Heit B. Quantitative Efferocytosis Assays. Methods in Molecular Biology: Phagocytosis and Phagosomes. 2017;1519:25-41. [Pubmed] [Article]

Announcing the RGE Murray Lecturer

RGE Lecturer - Dr. Chris Glass

Dr. Chris Glass

We are excited to announce the 2016/2017 RGE Murray Lecturer, Dr. Chris Glass, Professor of Cellular and Molecular Medicine and Professor of Medicine at the University of California, San Diego School of Medicine. Dr. Glass is a leader in the field of macrophage biology, and has made many seminar discoveries regarding the differentiation and specialisation of macrophages in response to various immunological stimuli and tissue environments.

Dr. Glass has published over 275 scientific papers, many in leading journals including Nature, Nature Immunology, eLife and Cell. Dr. Glass has been elected to the American Academy of Arts and Sciences (2014) and to the American Academy of Medicine (2015). He will be visiting Western University on January 27th, 2017. The time and location of his talk will be announced at a later date.

The RGE Murray Annual Lecture Seminar Series is supported by a generous donation made in the name of Professor Emeritus Robert G.E. Murray, and brings world leading immunologists, virologists and microbiologists to Western University. Dr. Murray served as department chair (1949 – 1974), is a founder of Canadian Society of Microbiologists, and in 1998 was invested into the Order of Canada in acknowledgement of his many contributions to science and the scientific community.

Cages – a New Plasma Membrane Structure

The Heit lab is excited to announce the discovery of membrane cages, a previously undescribed membrane structure.

Cages Abstract (click for full size)

Abstract of our new paper

This discovery has been published in the journal Scientific Reports. Membrane cages act to transiently block the diffusion of membrane proteins, thus structuring proteins in cellular membranes over short periods of time. This discovery was made, with our collaborator Dr John de Bruyn in the Department of Physics, through a combination of super resolution microscopy and classical cell biology techniques. We used high-speed super resolution microscopy to track the diffusion of CD93 – a macrophage receptor – and discovered that CD93 occasionally became trapped into membrane sub-regions that did not correlate to other known cellular structures. Through a range of experiments we were able to demonstrate that these “cages” were short lived (milliseconds to seconds), were independent of a previously described membrane structures, and that cages require cholesterol for their stability and strength.

Much remains to be discovered about the purpose and composition of this new cellular structure, but we expect cages to play an important role in structuring membrane proteins into functional units. Of particular interest to our lab is the negative impact of excess cholesterol on cages, an observation which suggests that some of the cellular deficiencies observed during diseases such as atherosclerosis (heart disease) may be a product of altered cage structure or function.

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Upcoming Events

December 15 2016
RGE Murray Seminar Series - Dr. Dan Wootton, University of Liverpool


January 6th 2017

Microbiology & Immunology 3300 - Immunology begins!


January 12th 2017
RGE Murray Seminar Series - Dr. Ravi Menon, Western University


January 19th 2017
RGE Murray Seminar Series - Dr. Byram Bridle, Univeristy of Guelph


January 27th 2017
RGE Murray Seminar Series - RGE Murray Lectureship - Dr.Christopher Glass, University of California (San Diego)


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