1. Antigens are toxic proteinaceous substances. However, polysaccharides and lipoproteins can also be antigens.
2. Its molecular weight is 10,000 daltons. But the best antigen has a molecular weight of 100,000 daltons.
3. It can bind to antibodies.
4. It may contain multiple epitopes or determinant groups.
5. Different organisms of the same species have species-specific antigens.
6. Organ specificity antigens are present in certain tissues or organs.

Antigens are toxic protein-like substances that bacteria release to weaken the host body

The immunity acquired by the transfer of antibodies from one body to another is called passive immunity. Passive defense is of two types. These are-

(i). Natural Passive Defence: Antibodies come from the mother’s body to the baby through colostrum and colostrum. It makes children immune to disease.

(ii). Artificial passive immunity: The body is made immune to disease by transferring antibodies from one body to another through injection.

The defense achieved through the production of antibodies in the body is called active immunity. Active defense is of two types. These are-

(i) Natural Active Defense: Infection occurs when humans are involuntarily exposed to microbes. All these germs are eradicated by naturally acquired abilities.

(ii) Artificial active immunity: Humans acquire this immunity through inoculation or vaccine. For example, DDP vaccine is taken for diphtheria, tetanus vaccine for scurvy and pertussis vaccine for whooping cough.

The ability to respond to microbes after birth is called acquired immunity. Acquired immunity is a specific immunity. It is of two types.

Active defense and passive defense

1. Active Immunity: The defense achieved through the production of antibodies in the body is called active immunity. Active defense is of two types. These are-

(i) Natural Active Defense: Infection occurs when humans are involuntarily exposed to microbes. All these germs are eradicated by naturally acquired abilities.

(ii) Artificial active immunity: Humans acquire this immunity through inoculation or vaccine. For example, DDP vaccine is taken for diphtheria, tetanus vaccine for scurvy and pertussis vaccine for whooping cough.

2. Passive Immunity: The immunity acquired by the transfer of antibodies from one body to another is called passive immunity. Passive defense is of two types. These are-

(i). Natural Passive Defence: Antibodies come from the mother’s body to the baby through colostrum and colostrum. It makes children immune to disease.

(ii). Artificial passive immunity: The body is made immune to disease by transferring antibodies from one body to another through injection.

1. Barriers: Human skin, alimentary tract, respiratory system, genital tract act as barriers.
2. Innate killer cells: Innate killer cells are a type of white blood cell or lymphocyte. It destroys virus infected cells and tumor cells.
3. Interferon: Interferon is a high molecular weight glycoprotein. It is produced by virus-infected cells and prevents the virus from multiplying.
4. Complement system: Complement system is a group of 20 types of plasma proteins. These inactive proteins are converted into active proteins that kill the bacteria.
5. Inflammatory response: Macrophages and neutrophils are activated and destroy the microbes.
6. Symbiotic bacteria: Symbiotic bacteria live in the body’s skin, genitals and digestive system. They destroy microbes by secreting chemicals.

Defenses that are acquired from the maternal body through immortality, are present in the body for life and are rapidly effective are called innate defenses. This is called genetic immunity.

Different types of innate defenses are-

1. Personal defense: When a person resists germs through his own immune system, it is called personal defense.
2. Species defence: Attacks by microbes are limited to specific species and only those specific species resist the pathogen. For example, the malaria parasite is limited to humans and mosquitoes.
3. Group immunity: If one group of people is infected by a parasite, the other group can easily resist it. For example, whites are more affected by tuberculosis than whites.

1. Arrival of phagocytes in the infected area (Infection): Chemicals such as histamine, kinin, prostaglandin are produced in the infected area of ​​the body. Due to these chemicals, phagocyte cells (macrophages and neutrophils) are stimulated and accumulate at the wound site. This process is called chemotaxis.
2. Adherence to microbes: Phagocyte cell membrane contains receptor material. Phagocytes attach to microbes with the help of receptor substances.
3. Germ eating (Ingestion): Phagocytes surround the germs by making passageways. The cavity formed in it is called phagosome. Phagocytes ingest microbes by forming phagosomes.
4. Formation of phagolysosome (Phagolysome): Phagosomes are located individually in the cytoplasm of the cell. Lysosomes fuse with phagosomes to form sac-like structures. It is called phagolysosome.
5. Bacterial death and digestion (Killing): Inside the phagolysosome, the lysosome secretes bactericidal proteolytic enzymes. This enzyme destroys bacteria. Bacteria die within 10-30 minutes of ingestion.
6. Discharge: After destroying the bacteria, the neutrophils die and are released as pus. Macrophages destroy new bacteria by releasing toxic and indigestible parts.

The term phagocytosis is derived from the Greek words phagein meaning to eat, kytos meaning cell and oisis meaning process. It means cell eating method. The process in which different types of white blood cells keep the body healthy by eating or destroying microbes that enter the body is called phagocytosis.

Macrophages are large white blood cells. When the blood monocyte cells increase in size by 5 times, they are called macrophages or large eaters. Transformed macrophages are active phagocytic cells. Macrophages accumulate at infected sites of cells. Its opsonin substances identify microbes. Macrophages then release hydrolytic enzymes and cytokines. These chemicals destroy germs. A macrophage can ingest 100 bacteria. Macrophages remain active for several months after ingestion.

Macrophages can also consume larger organisms such as fungi and malaria. Cytokines released from it recruit the necessary cells to heal the wound. The chemical increases the rate of the phagocytosis process.