The immune system is responsible for the ability of a host to resist foreign invaders. It includes an array of cells and molecules with specialized roles in defending the host against the continuous onslaught of microbes, toxins, and cancer cells.

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THER ARE TWO TYPES OF IMMUNITY ; UNSPECIFIC/NATURAL AND SPECIFIC/ADAPTIVE IMMUNITY.
WE WILL BE DISCUSSING SOME KEY TERMS AND PROCESSES OF THE LATTER TODAY.

The adaptive /specific immune response is antigen-specific and requires the recognition of specific "non-self" antigens during a process called antigen presentation

The major function of the specific immune response in vertebrates is to provide protection (immunity) against antigens such as harmful microorganisms,toxins,and abnormal (cancer) cells through the recognition and destruction of these foreign (non-self)materials.

What are Antigens?

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Antigens are substances, such as proteins, nucleoproteins, polysac￾charides, and some glycolipids, to which lymphocytes respond.

Specific (adaptive) immunity is of types:

#Humoral and #cell #mediated

• Cell-mediated immunity involves specialized white blood cells called T cells that act against microbe-infected cells and foreign tissues.
  They also regulate the activation and proliferation of other immune system cells such as macrophages, B cells, and
  other T cells.

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(Image of a Tcell)

• Humoral immunity, or antibody-mediated immunity, involves the production of glycoprotein antibodies by plasma cells
  derived from B cells.
  In order to function,B and T cells must be exposed to a specific anti￾gen and other required signals. This results in their proliferation
  and differentiation in a process known as clonal selection.

Activated T cells produce cytokines that assist in the development
and function of other immunocytes.
Activated B cells produce antibody, also called immunoglobulin.

What are immunoglobulins ?

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Immunoglobulins also known as antibodies, are glycoprotein molecules produced by plasma cells (white blood cells).

They act as a critical part of the immune response by specifically recognizing and binding to particular antigens, such as bacteria or viruses, and aiding in their destruction. They respond to invasion by foreign antigens and that protect the host by removing pathogens; an antibody

Types of immunoglobulin or (Ig)

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There are five human Ig classes based on physicochemical and biological properties these are : IgG, IgM, IgD, IgA, and IgE.

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Effects of antigen and antibody reactions.

• The binding of antigen to antibody forms a complex called: ANTIGEN-ANTIBODY COMPLEX and this initiates the participation of
  other elements that determine the fate of the antigen.
  For example, the classical complement pathway can be activated,
  leading to lysis or phagocytosis of antigens.

Other defensive mecha￾nisms include toxin neutralization, adherance inhibition, and
opsonization.

IMMUNE DISORDERS

• > Immune disorders range from mild conditions like hay fever to life threatening diseases.

They can be categorized as

• hypersensitivi￾ties
• autoimmune diseases
• transplantation (tissue) rejection and
• immunodeficiencies.

Specific immunity is acquired and requires
sufficient time to fully develop. However, upon subsequent expo￾sure to the same substance, activation of a specific immune response is significantly faster and stronger than that of the initial
response. Thus the cooperation between the host’s innate resistance
mechanisms and its specific killing responses prevents pathogen
invasion and maintains host integrity through the combination of
immediate, nonspecific resistance and delayed, specific responses.

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