Immune System | Types of Immunity

The immune system is a complex network of cells and proteins that defends the body against infection. The immune system keeps a record of every germ (microbe) it has ever defeated so it can recognize and destroy the microbe quickly if it enters the body again.

Types of Immune Response

  1. Nonspecific Immune Response
  2. Specific Immune Response

Nonspecific Immune Response

It is directed against invading microbes. The examples of nonspecific immune response includes Physical barriers and bloodbourne nonspecific immune response

Physical Barriers includes

1.Body surface barriers: intact skin and mucosa, cilia, and mucus secretions

2. Antimicrobial secretions: oil of skin, tears, gastric juice, and vaginal secretions

Bloodbourne Nonspecific Immune Response includes

1. Internal antimicrobial agents

a. Interferon: It is a substance produced within cells in response to viral attack

b. Properdin (Factor P): It is a protein agent in blood that destroys certain gram-negative bacteria and viruses

c. Lysozyme: destroys mainly gram-positive bacteria

2. Phagocytes (monocytes, macrophages, Natural Killer Cells, Dendritic cells): cells that ingest and destroy microbes; part of the reticuloendothelial system

3. Inflammatory response

 First stage: the release of histamine and chemical mediators (e.g., prostaglandin, bradykinin) leads to vascular dilation and increased capillary permeability, resulting in signs of inflammation (e.g., pain, heat, redness, edema, and loss of function)

Second stage: exudate production

Third stage: reparative phase

Specific immune response

It directed against a specific pathogen (foreign protein) or its toxin; may be cell-mediated or humoral

Cell-mediated immunity (T-cell immunity)

  • Occurs within cells of the immune system
  •  Involves T lymphocytes (e.g., T helper, T suppressor, T cytotoxic, lymphokines); each type plays a distinct role in immune response
  • Cluster designations: mature T cells carry markers on the surface that permit them to be classified structurally (e.g., CD4 cells associated with acquired immunodeficiency syndrome [AIDS])

Functions of cell-mediated immunity

  • Protect against most viral, fungal, protozoan, and slow-growing bacterial infections
  •  Reject histoincompatible grafts
  • It causes skin hypersensitivity reactions (e.g., tuberculosis [TB] screening)
  • Assists with diagnosis of malignancies

Humoral immunity (B-cell Immunity)

  • It concerned with immune responses outside of cell
  • It involves B lymphocytes that differentiate into plasma cells and secrete antibodies


  • Immune substance produced by plasma cells;
  • Antibodies are gamma globulin molecules;
  • Antibodies are commonly referred to as immunoglobulin (Ig)


Any substance, including allergen, that stimulates the production of antibodies in the body

Typically, antigens are foreign proteins, most potent being microbial cells and their products


  • Complement is a group of blood serum proteins needed in certain antigen-antibody reactions;
  • Both complement and antibody must be present for the reaction to occur

Immunoglobulins (Antibodies)

There are five types of immunoglobulins in our body. They are:-

  • IgM
  • IgG
  • IgA
  • IgE
  • IgD

Immunoglobulin M (IgM) antibodies:

It is a first antibodies to be detected after exposure to antigen; protection from gram-negative bacteria

Immunoglobulin G (IgG) antibodies:

  • It makes up more than 75% of total immunoglobulins;
  • The highest increase in response to subsequent exposure to antigen;
  • The only immunoglobulin that passes the placental barrier

Immunoglobulin E (IgE) antibodies

  • It responsible for hypersensitivity and allergic responses;
  • It causes mast cells to release histamine;
  • It helps to protect from parasites

Immunoglobulin A (IgA) antibodies

It present in blood, mucus, and human milk secretions; play important role against viral and respiratory pathogens

Immunoglobulin D (IgD) antibodies

It helps to differentiate B lymphocytes

Types of Humoral Immunity

Mainly Two Types

  1. Active Immunity
  2. Passive Immunity

Active Immunity

It means antibodies formed in body.

It is two types

  • Natural Active Immunity
  • Artificial Active Immunity

Natural active immunity

It means antibodies formed during course of disease; may provide lifelong immunity (e.g., measles, chickenpox, yellow fever, smallpox

Artificial active immunity

The vaccine or toxoid stimulate formation of homologous antibodies; revaccination (booster shot) often needed to sustain antibody titer (anamnestic effect)

Artificial Active Immunity Produced by Administration of:-

a. Live vaccines: antigenic preparations containing weakened (attenuated) microbes; typically such vaccines are more antigenic than killed preparations (e.g., oral [Sabin] poliomyelitis vaccine, measles vaccine)

b. Killed vaccines: antigenic preparations containing killed microbes (e.g.,pertussis vaccine, typhoid vaccine)

c. Toxoids: antigenic preparations composed of inactivated bacterial toxins (e.g., tetanus toxoids, diphtheria toxoids)

Passive immunity

Antibodies acquired from outside source produce short-term immunity

It is also two types;

  • Natural Passive Immunity
  • Artificial Passive Immunity

Natural passive immunity

  • It is the passage of preformed antibodies from mother through the placenta to fetus or through the colostrum to neonate;
  • During the first few weeks of life, the newborn is immune to certain diseases to which the mother has active immunity

Artificial passive immunity

  • It is acquired by injection of antisera derived from immunized animals or humans;
  • It provides immediate protection and also is of value in treatment (e.g., diphtheria antitoxin, tetanus antitoxin)
Immune system

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