Innate vs. Adaptive Immunity: A Comparison

December 15, 2023
A graphic of a person and pathogens

Innate immunity and adaptive immunity are two types of immune responses that help to protect the body against infections and other harmful substances.

Innate immunity is the body’s first line of defense against infections and other harmful substances. It is the body’s natural, nonspecific immune response, and it is activated immediately upon encountering a pathogen or other foreign substance. Innate immunity includes physical and chemical barriers, such as the skin and mucous membranes, as well as immune cells, such as neutrophils and macrophages.

Adaptive immunity, also known as acquired immunity, is a more specific and slower-acting immune response that is activated after the body has been exposed to a pathogen or other foreign substance. Adaptive immunity involves activating T cells and B cells, which recognize and attack specific pathogens or other foreign substances. Adaptive immunity also includes the production of antibodies, which are proteins that specifically target and neutralize pathogens or other foreign substances.

In summary, innate immunity is a nonspecific, immediate immune response that provides the body’s first line of defense against infections and other harmful substances. Adaptive immunity is a specific, slower-acting immune response that is activated after the body has been exposed to a pathogen or other foreign substance, and it involves the activation of T cells and B cells and the production of antibodies.

What Is The Immune System?

The immune system defends the host (you) against pathogens such as bacteria, fungi, viruses, and protists. Specific types of these organisms cause disease in humans. The immune system must be able to detect pathogens, distinguish them from host cells, and get rid of them. The immune system also detects cancerous and damaged cells. To accomplish this, the immune system has two layers of defenses: the innate and adaptive immune systems.

Your body cells have surface proteins on them that are part of a complex called the major histocompatibility complex. These proteins are like flags on the surface of your cells that tell your immune system that these are “self” cells, not invaders. When your immune system inadvertently attacks “self” cells, it is autoimmunity.

What Is Innate Immunity?

The innate immune system is a fast, nonspecific, but temporary immune response that can be divided into barrier, chemical, and cellular defenses. When a known pathogen invades, the innate immune system starts sluggishly from scratch each time.1

Barrier Defenses

Mechanical barriers physically prevent pathogens from entering the body. The innate immune system provides the first line of defense against invading pathogens. It includes a number of physical, chemical, and biological barriers that prevent pathogens from entering the body or spreading throughout the body. Some of the key barrier defenses in the innate immune system include:

  1. Skin: The skin is a physical barrier that protects the body from external threats, such as bacteria and viruses. It also produces oils and sweat that contain antimicrobial substances that can inhibit the growth of pathogens. Sebaceous glands secrete sebum onto the surface of the hair and skin. Sebum forms a thin, slightly acidic film over the skin’s surface that acts as a barrier to pathogens.
  2. Mucous membranes: Mucous membranes, such as those found in the respiratory, gastrointestinal, and genitourinary tracts, produce mucus that traps and removes pathogens. Cilia, tiny hairlike structures, also help to sweep mucus and trapped pathogens out of the body. Sneezing and coughing also help to eject pathogens. Urine and vaginal secretions are acidic. Semen contains zinc and defensins that disrupt membranes on the surface of bacteria.
  3. Stomach acid: The acidity of the stomach (pH of around 2) helps to kill many types of bacteria and viruses that are ingested.
  4. Tears and saliva: Tears and saliva contain antimicrobial substances, such as lysozyme, which can help to kill or inhibit the growth of bacteria and viruses.
  5. Commensal bacteria: The body is home to trillions of microorganisms, many of which are beneficial and help to keep harmful pathogens in check. For example, the gut microbiome helps to prevent the colonization and proliferation of harmful bacteria in the gastrointestinal tract.

Chemical Defenses

If pathogens breach the barrier defenses, they will trigger an inflammatory response. Inflammation is triggered by chemicals released by injured or infected cells. These chemicals cause increased blood flow and leakiness in blood vessels and direct infection-fighting cells to the infected area.

The signs and symptoms of inflammation include the following:

  • Redness
  • Swelling
  • Warmth
  • Pain
  • Some loss of function

The complement system is a complex system that, when activated, coat pathogen surfaces with protein fragments, targeting them for destruction.

Cellular Defenses

Innate immune cells are phagocytes (commonly thought of as the Pac-men of the immune system). They engulf and digest pathogens. Some phagocytes patrol throughout the body, and some reside in specific tissues. Digestive enzymes and acids located in vesicles in the phagocyte will kill and digest the pathogen.

White blood cells called leukocytes serve many functions in the innate immune system.

  • Neutrophils: phagocytic cells that are usually the first to arrive at infection and help direct other cells to the area. They are the most numerous type of white blood cells and are responsible for eliminating bacteria and fungi.
  • Macrophages: phagocytic cells produce a wide range of chemicals, phagocytize pathogens and damaged host cells, and present antigens to activate the adaptive immune system.
  • Eosinophils: non-phagocytic cells that help defend against parasites.
  • Basophils: non-phagocytic cells that release histamines and heparin. Histamine dilates blood vessels and increases their permeability as part of the inflammatory process. Heparin helps prevent blood clotting.
  • Dendritic cells: phagocytic cells that develop from monocytes that are typically found in the skin, nose, lungs, stomach, and intestines. Dendritic cells also present antigens to the adaptive immune system.
  • Mast cells: non-phagocytic cells that secrete histamine and are involved in inflammation and allergic reactions.
  • Natural killer cells: a subset of lymphocytes that destroy cancer cells or virally infected cells. Natural killer cells look for “self” cells with low levels of major histocompatibility complex (MHC) proteins. These cells may be infected or cancerous.

The innate response is the more primitive of the two branches of the immune response. The imprecise and sluggish targeting by the innate immune system can wreak havoc on your body’s tissues.1 The adaptive immune system provides a more controlled response.

A woman giving pills to a sick man.

What Is Adaptive Immunity?

The adaptive immune system consists of specialized cells and processes targeting specific pathogens. The adaptive immune system is designed to recognize and remember specific pathogens so follow-up responses can be faster, stronger, and more comprehensive.

Cells in the adaptive immune system are lymphocytes. The two main types of lymphocytes are T cells and B cells. T cells destroy infected cells and release chemicals that regulate the immune system. B cells secrete antibodies that bind with antigens on pathogens to mark them so they are easier for other immune cells to remove. Each lymphocyte expresses one or at most a few receptor types, which means that only pertinent lymphocytes are activated, and they detect the slightest distinction between self and non-self cells.1


There are multiple types of T cells. The two major classes are helper T cells and cytotoxic T cells. After a macrophage phagocytizes a pathogen, a part of the pathogen is displayed on the macrophage’s surface as a flag. These cells are called antigen-presenting cells and play an important role in activating T cells.

Helper T cells

CD4+ T cells are also known as T helper cells. They are activated by dendritic cells, which present antigens (proteins on the surface of pathogens) to them. Once activated, CD4+ T cells secrete cytokines (small proteins that help to coordinate the immune response) and help to activate other immune cells, such as B cells and macrophages. Once helper T cells are activated, they help direct the innate and adaptive immune systems.

Killer T cells

CD8+ T cells or killer T cells (cytotoxic T cells) destroy cells that have non-self-antigens on their surface. They recognize and kill cancerous or infected cells by releasing toxic chemicals, such as perforin and granzymes.

Regulatory T cells

Regulatory T cells help regulate the immune response and prevent autoimmune diseases, which are conditions in which the immune system attacks healthy cells in the body.


B cells create antibodies, which are large, Y-shaped proteins that identify and neutralize foreign invaders. B-cells may also serve as antigen-presenting cells and secrete chemicals.

B cells must be activated first. This occurs when the B cell engulfs and digests an antigen. The antigen may be free-floating or on the pathogen. B cells internalize the antigen and present it to helper T cells. The helper T cells then secrete cytokines that stimulate B cells to multiply and produce plasma cells and memory B cells. Plasma B cells produce antibodies. Antibodies binding to antigens make it easier for phagocytic cells to find and destroy them. Memory B cells remain in the body after an infection and can provide long-lasting immunity by producing large amounts of antibodies if the same pathogen is encountered a second time.

Upon encountering antigens displayed on a pathogen they recognize, lymphocytes proliferate extensively to maximize their fighting power and differentiate into subsets of cells to allow for an even better-targeted response.

Graphic of the circulatory and lymphatic systems.

What About The Lymphatic System?

The lymphatic system includes organs such as the thymus, spleen, hundreds of lymph nodes, and the lymphatic vessels connecting them. These organs provide a haven for lymphocytes to be produced, undergo a complicated maturation process, and reside until they are ready to fight infections.

B cells mature in the bone marrow and then enter the lymphatic system to search for pathogens. T cells mature in the thymus. Bone marrow and the thymus are primary lymphoid organs because the lymphocytes mature there.

The tonsils, spleen, and lymph nodes are secondary lymphoid organs. They store lymphocytes and filter lymph. It is in secondary lymphoid organs that lymphocytes encounter pathogens, which activate them and initiate their adaptive responses. Chemicals secreted by immune cells, known as chemokines and adhesion molecules, bring immune cells together at the right time and place.2

What Is The Main Difference Between Innate And Adaptive Immunity?

Innate immunity and adaptive immunity are two types of immune responses that help to protect the body against infections and other harmful substances. The main difference between the two is the nature of the immune response and the speed at which it is activated.

Both types of immunity are essential and are linked in their processes. The phagocytic cells in the innate immune system capture pathogens, cut them up into small molecular pieces of proteins, and present these antigens to the lymphocytes. These antigen-presenting cells link innate and adaptive immunity.

A sick older women

How Does Aging Affect The Immune System?

Aging is associated with several changes in the immune system that can affect its function and increase the risk of infections and autoimmune diseases. This decline in immune function is called immunosenescence. Some of the key ways in which aging affects the immune system include:3,4

  1. A decline in barrier protection: Skin as a barrier becomes less effective with aging with decreased skin cells, sweat production, and immune cells, and loss of subcutaneous tissue. Immunoglobulin A (a protectant for mucous membranes) production declines after age 60.
  2. Decline in immune cell production: The bone marrow, which is responsible for producing immune cells, becomes less efficient at producing new immune cells as we age. This can lead to a decrease in the number and function of immune cells.
  3. Decreased effectiveness of immune responses: As we age, the immune system becomes less effective at mounting an immune response to pathogens and vaccines. This can make older individuals more susceptible to infections and less responsive to vaccines.
  4. Increased inflammation: Aging is associated with an increase in chronic low-grade inflammation, which can lead to tissue damage and a greater risk of chronic diseases, such as heart disease and cancer.
  5. Changes in the microbiome: The microbiome (the collection of microorganisms that live in the body) changes as we age, which can affect the immune system. For example, a decrease in the microbiome’s diversity has been linked to an increased risk of infections and chronic diseases.

Overall, aging is associated with many changes in the immune system that can affect its function and increase the risk of infections and chronic diseases. However, there are ways to help maintain a healthy immune system, such as eating a balanced diet, getting regular exercise, and getting enough sleep.

How Can You Boost Your Immune System?

Your immune system is a complex, hard-working system that protects you against pathogens. Any lifestyle changes you can make to reduce strain on your immune system may pay off with a decreased risk of chronic diseases due to low-grade inflammation or an increased risk of frequent infections. While scientific evidence does not support the premise that lifestyle changes can improve your immune system, optimizing your overall health is sure to allow your immune system to function at its full potential.

Consume A Nutritious Diet

Consume a nutritious, balanced diet to provide your immune system with the vitamins and minerals it needs to function at its best. Choose from a wide array of fresh fruits and vegetables, whole grains, legumes, low-fat dairy products, and lean meats. Drink plenty of fluids.

Eat foods rich in5

  • Vitamin A: dairy products, eggs, fish, orange and red vegetables, and fruits
  • Vitamin C: citrus fruits, kiwis, berries, broccoli, tomatoes, spinach, and red peppers
  • Vitamin E: olive oils, olives, unsalted nuts, avocado
  • Iron: meats, fish, shellfish, eggs, green leafy vegetables, lentils, and dried fruits
  • Zinc and selenium: legumes and whole grains
  • Omega-3 fatty acids: oily fish, nuts, and green vegetables

Avoid consuming ultra-processed foods, excessive alcohol, refined sugar, salt, and saturated fats.

Foods for the immune system

Get Plenty Of Sleep

Activation of the immune system alters sleep, and sleep affects how well both arms of the immune system function. When you are sick, the immune system activates the inflammatory pathway, which can induce and increase sleep duration and intensity or disrupt sleep. Prolonged sleep deficiency can also induce chronic, systemic, low-grade inflammation, which is associated with many chronic diseases such as diabetes, atherosclerosis, cardiovascular disease, asthma, and neurodegeneration.6

Sleep is necessary to strengthen the immune response after vaccination, maintain overall immune health, fight pathogens and reduce the risk of complications from infections, and decrease the risk of chronic diseases associated with low-grade inflammation.6

Make Exercise A Priority

Exercise and even movement throughout the day can improve overall health and support immune function. Exercising in moderation is the key. Overexertion for long periods can actually suppress immune function. Exercise can increase the circulation of immune cells, which can help them reach sites of infection more quickly and reduce inflammation.

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Author: Leann Poston, M.D.
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