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How The Body Reacts To Viruses

Learn with Harvard Medical School faculty about how the body fights disease.

We live in a microbial world, which means that we constantly encounter microorganisms that could harm our health. The human immune system continuously defends us against these threats to our survival. Understanding how immunity works is important for making sense of the news around the risk, spread, and treatment of diseases like COVID-19 (also known as coronavirus disease).

In this curated selection of videos and interactive materials from HMX Immunology courses, you’ll learn about the processes that enable our immune system to respond to microbial threats.

Please note: HMX online courses in immunology are primarily designed for those working in areas related to health care and the immune system, including diagnostics and treatments. Given the current situation, we’ve decided to make relevant material available to all. We understand that not everyone may have the appropriate background, and we encourage you to use other resources as needed to understand any unfamiliar terms and get the most from this material.


An Immune System for our Microbial World

In this video, you will see a high-level overview of the immune system at work in the context of daily life. What is seen here equally applies to transmission and the body’s reaction to a coronavirus. The immune system mounts a response against pathogens as they infect an individual and replicate. The response includes both an immediate innate response and a slower adaptive response, which are explained in greater detail in the following sequence. This video features HMX Fundamentals Immunology faculty member Andrew Lichtman of Harvard Medical School.

Introduction to the Innate Immune Response

The innate immune response forms the first line of defense against invading pathogens. Innate immunity includes barriers and a variety of cells and molecules that are part of the rapid response to threats to our health. In this interactive you will be introduced to the various aspects of the innate immune response and the ways in which they work together to prevent and control infection. While the immune system protects us from many pathogens, the inflammation that occurs as part of the immune response can also damage our own tissues and impair the function of our organs when pathogens stimulate a very strong response.

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Innate Immune Responses to Microbes

Now that you understand the basics of how the innate immune response works, you’re ready to look at an example. In this interactive, you will learn how the innate immune response acts against an invading pathogen. Innate immunity can help protect us from a variety of pathogens, including the coronavirus that causes COVID-19, though the specifics and the efficacy of the response can differ depending on the type of pathogen.

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Introduction to B Cells and Antibodies

While the innate immune response is able to prevent or control some infections, it is limited in the ways in which it can react. The adaptive immune response, which includes both B cell-based humoral immunity and T cell-based cellular immunity, reacts much more specifically and powerfully to invading pathogens. B cells produce antibodies that help to control microbial invasion in a variety of ways, as described in this interactive.

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B Cell Responses to Bacteria

With your new knowledge about antibodies, you are ready to see an example of the B cell response in action. In this interactive, the reaction of B cells to an invading pathogen is shown, including how the antibody response arises and how it is able to control the infection. While the response to a bacterial protein is shown, the steps necessary to act against viruses such as the coronavirus that causes COVID-19 are very similar. Antibody responses are the main way in which vaccines protect us from infection by a variety of viruses, and the absence of protective antibodies contributes to the rapid spread of new viruses in previously unexposed and unvaccinated populations.

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What Do T Cells See?

The antibodies produced by B cells form part of the adaptive immune response and can recognize almost any molecule that might invade the body. In addition, there is a second branch to the adaptive immune system called cellular immunity. T cells form the basis of cellular immunity and can very specifically kill cells that have been infected by viruses. This video compares the two branches of the adaptive immune response, with a particular emphasis on the antiviral effects of T cells. This video features HMX Fundamentals Immunology faculty member Shiv Pillai of Harvard Medical School.

Introduction to the T Cell Response

T cells form the second branch of the adaptive immune response. Unlike B cells, the receptors on T cells are only able to recognize protein fragments displayed on specific cell surface molecules. In this interactive, you will learn about the different types of T cells, including cytotoxic T cells that kill infected cells and helper T cells that increase the activation of other immune cells.

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T Cell Responses to Viral Infections

While the innate immune and B cell responses are effective against a wide variety of pathogens, T cells can respond very specifically to intracellular pathogens, such as viruses. In this interactive, you will walk through an example of a T cell response to a viral invasion, as would occur in the case of COVID-19.

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Looking for a more in-depth online learning experience? Our foundational immunology course covers key concepts in the field. If you’d like to understand the latest developments in protecting against viral infections, consider our advanced course on vaccines and viral immunology.

HMX Fundamentals Immunology instructors Andrew Lichtman and Shiv Pillai have also shared their thoughts about the importance of understanding immunology and what the science tells us about reducing transmission of SARS-CoV-2.

Looking for more information specific to the coronavirus? Please see the Coronavirus Resource Center from Harvard Health Publishing.