NATURAL & ACQUIRED IMMUNITY

Introduction

Immunity is the resistance or insusceptibility of the body against antigens and infections or pathogenic organisms and their biological products.

It has both specific and non-specific. 2 category

1. Innate immunity or non-specific immune system or in-born immunity system

2. Acquired immunity or adaptive immunity or specific immunity

Innate immunity : the immune system is present at the birth and changes little throughout the lifetime of the individual.

The cells and molecule of the innate system are mainly responsible for the first stage of expulsion of the microbe and may give rise to inflammation.

Innate immune system1. species specific innate immunity 2. individual specific innate immunity

Species specific innate immunity

Human beings are naturally resistant to Distemper virus , which causes 30-50 % death in dogs.

Birds are immune to tetanus , which fatal to human beings. Birds are also immune to anthrax , because of their high body

temperature , the inhibit the growth of the pathogen.

Individual specific innate immunity

Some differences in individuals of the same species occur with regard to susceptibility for certain infection.

Sickle cell anemia and thalassemia patients are resistant to malaria .

Individuals of blood group O & B are more resistant to small pox than those of blood group A.

Mechanism of natural immunity

The innate immunity can be seen to comprise four types of defensive barriers

1. Anatomic barriers2. Physiological barriers3. Phagocytic barriers4. Inflammatory barriers

Anatomic barriers

Physical & anatomic barriers that prevent the entry of pathogens are an organisms first line of defense against infection.

The skin and mucous membranes are included in this category. The epidermal layer consists of epithelial cells of several layers

with a protein keratin. The sebum consists of lactic acid & fatty acids , which maintain

the pH of the skin between 3 & 5 this inhibit the growth of most micro organisms.

The cilia in the respiratory tract and gastrointestinal tract propel mucous entrapped microorganisms.

Body Coverings: The Skin

sebaceous glands

sweat gland

epidermis

Physiologic barriers

Physiologic barrier that contribute to innate immunity include temperature , pH and various soluble factors.

A variety of soluble factors contribute to non-specific immunity includes that soluble proteins , lysozyme , interferon and complement.

Interferon comprises a group proteins produced by virus infected cells.

The function of interferon is the ability to bind to nearby cells and induce a generalized antiviral state.

Complement is a group of serum proteins that circulate in an inactive state.

Phagocytic barriers

Another innate defense mechanism is the ingestion of particulate matter by phagocytosis.

Specialized cells such as blood monocytes , neutrophil and tissue macrophages , do mostly phagocytosis.

Most cell types are capable of endocytosis such as receptor – mediated endocytosis.

Inflammatory barriers The tissue damage caused by a wound or by an invading pathogenic

organisms induce a complex sequence of events collectively known as the inflammatory response .

1. Vasodilation : an increase in diameter of blood vessels. 2. Edema :Dilutes harmful substances

Provides nutrients (& O2) for repair Enhances entry of clotting protein

3.Phagocytic cells accumulate at the site begin to phagocytose bacteria , they release lytic enzymes , which can damage nearby healthy cell

The accumulation of dead cells , digested material & fluid forms a substance called Pus.

Inflammatory Response

Histamine & prostaglandins released

Capillaries dilateClotting begins

Chemotactic factors attract phagocytic cells

Phagocytes consume pathogens & cell debris

Acquired immunity ( adaptive immunity or specific

immunity ) Adaptive or specific immunity is capable of recognizing and selectively

eliminating specific antigens.

The adaptive immune responses are reactions to specific antigenic challenges and display 4 important attributes:

1. Antigenic specificity :The antigenic specificity of the immune system permits it to distinguish subtle differences among antigens.

2. Diversity :capable for generating tremendous diversity in recognition molecule. For foreign antigen.

3. Immunologic memory :the immune system has recognized & responded to an antigen it exhibit immunologic memory .

4. Self / non self recognition : finally the immune system normally responds only to foreign antigens

Cells Involved In Acquired Immunity

There are 3 major cell types involved in acquired immunity .1. T cells 2. B cells3. Antigen presenting cells such as

# Macrophages# Dendritic cells

Thank YouBy

Anand P P