Basic Concepts of Immune Response

Basic Concepts of Immune Response

Immune response is the body’s ability to recognize, respond to, and eliminate foreign substances (antigens).

Innate immunity is the body’s inherent, genetically determined ability to defend itself.

Sensitization is the process by which the body comes into contact with a foreign antigen.

Physical barriers are the body’s first line of defense, including skin and mucous membranes.

The role of physical barriers is to separate the body’s internal environment from the external environment.

Mucous membranes are layers of elastic cells covered with a layer of mucus.

Mucous membrane mucus is secreted from glands beneath the mucous membrane, creating a protective barrier that prevents bacteria and foreign substances from directly attaching to cells.

Direct attachment of bacteria to cells is a prerequisite for them to penetrate deeper into the body.

Innate immunity has 4 protective mechanisms:

• Physical barriers: Including skin and mucous membranes, preventing the entry of antigens.

• Chemical barriers: Including internal fluids, blood serum, containing lysozyme, C-reactive protein (CRP), complement components, interferon, etc.

• Cellular barriers: Including cells capable of phagocytosis, such as neutrophils and macrophages.

• Physical barriers: The synthesis of all morphological and functional characteristics of the body, creating differences between species and individuals.

Cellular barriers are the most complex and important mechanism in the protective measures of the innate immune response.

Skin hinders the entry of antigens due to the keratinized layer (the outermost layer of cells) that constantly sheds and regenerates.

Mucous membranes prevent the entry of antigens by being highly elastic and covered with a layer of mucus, preventing bacteria from attaching directly to cells.

Mucous membranes of the eyes, mouth, etc. are washed clean by thin secretions.

Mucous membranes of the respiratory tract have microvilli that constantly vibrate, blocking dust carrying bacteria and foreign substances from entering the alveoli and pushing them out of the bronchi by coughing and sneezing reflexes.

Bacteria cannot survive long on the skin due to secretions such as lactic acid (creating acidity), fatty acids (from sweat and subcutaneous fat glands).

Secretions from glands such as tears, saliva, nasal mucus, milk contain high levels of lysozyme, which affects the shell of some bacteria.

After passing through the skin and mucous membranes, the antigen will encounter chemical barriers inside the body, which are internal fluids, blood serum, containing lysozyme, C-reactive protein (CRP), complement components, interferon, etc.

C-reactive protein is a protein that binds to phosphorylcholine in the C carbohydrate of pneumococci. It is produced by the liver and has elevated levels in acute inflammation. It acts on pneumococci, fixing complement.

Interferon (INF) is a family of proteins produced by various cell types, mainly NK (natural killer) cells. It has the property of non-specifically fighting viruses, hindering the entry and replication of viruses.

Virus-infected cells can produce interferon, which diffuses into surrounding cells to help them not be infected. Interferon produced will stimulate uninfected cells to synthesize specific enzymes to destroy viral RNA, inhibiting the protein synthesis process of the capsid shell.

The role of interferon: Prevents virus entry, inhibits reverse transcription ability, virus biosynthesis.

Cellular barriers consist of various cell types, but mainly cells capable of phagocytosis, including two types: neutrophils and macrophages.

Phagocytic cells are not only present in internal fluids, in the blood but also in large numbers on mucous membranes (transported from internal fluids).

The origin of macrophages and neutrophils is the bone marrow.

Neutrophils are polymorphonuclear leukocytes, can only kill small antigen types and die shortly after.

Macrophages differentiate into monocytes in the blood, then migrate to tissues –> become cells of the reticuloendothelial system.

The process of phagocytosis is divided into 3 stages:

• Adhesion stage: The phagocytic cell binds to the antigen.

• Engulfment stage: The phagocytic cell engulfs the antigen inside.

• Digestion stage: The phagocytic cell destroys the antigen.

During phagocytosis, microorganisms are destroyed by two mechanisms:

• Oxygen-dependent mechanism: Forms free radicals.

• Oxygen-independent mechanism: Due to proteolytic enzymes, hydrolytic enzymes…

Physical barriers are the synthesis of all morphological and functional characteristics of the body. It creates differences between species and species, between individuals and individuals against the attack of foreign substances.

Non-specific inflammation is a circulatory and cellular manifestation with symptoms of swelling, heat, redness, pain, aiming to destroy and eliminate invading agents.

Acquired immunity (or specific immunity) is the immune state that appears when the body has had contact with the antigen (the antigen is introduced actively or randomly). It can also be acquired when antibodies or immune-competent cells are transferred into the body.

The specific immune response system eliminates foreign antigens by two methods:

• Humoral immune response: Producing specific antibodies to neutralize or destroy antigens.

• Cell-mediated immune response: Using immune cells to destroy virus-infected or cancerous cells.

Both immune response methods (humoral and cell-mediated) go through 3 steps:

1. Antigen recognition step: Immune cells recognize and bind to the antigen.

2. Activation step: Immune cells are activated to produce antibodies or perform cell-killing functions.

3. Effect step: Antibodies or immune cells perform their function of eliminating antigens.

Specific inflammation occurs when the body has been sensitized (has been in contact with the antigen and has humoral or cellular antibodies). It is the combination of antigen and antibody.

If humoral antibodies are the main factor, inflammation is usually acute, occurring quickly.

If the antigen is only sensitized to T lymphocytes, the inflammatory response occurs slowly. The release of lymphokines attracts and concentrates white blood cells to the inflammatory focus to destroy the inflammatory agent.

Basic characteristics of SPECIFIC IMMUNE RESPONSE:

1. Specificity: Antibodies (humoral or cellular) are specific to a certain group of antigen determinants (called antigen epitopes).

2. Diversity: The number of antigen epitopes in nature is extremely large, yet the body still has enough specific antibodies for each type —> due to the diversity in the structure of the antibody receptor part.

3. Immune memory: The immune response is stronger in intensity, shorter in latency, and longer in duration of response each subsequent time.

4. Regulation: The immune system self-regulates through information secreted by cells such as adhesion molecules, cytokines, Igs…

5. Ability to distinguish the nature of antigens: Eliminate foreign antigens and do not react with self-antigens.

Classification of specific immunity:

• Active immunity: Immunity produced by the body itself when it has been in contact with the antigen.

• Natural active immunity: Generated when the body comes into contact with a natural antigen, such as contracting a disease.

• Artificial active immunity: Generated when the body comes into contact with an artificially introduced antigen, such as vaccination.

• Passive immunity: Immunity when antibodies are introduced from the outside (not produced by the body).

• Natural passive immunity: Generated when the body receives antibodies from the mother through the placenta or breast milk.

• Artificial passive immunity: Generated when the body is given antibodies from another person or animal.