INTRODUCTION TO IMMUNOLOGY - Lecture Notes

INTRODUCTION TO IMMUNOLOGY

Ms. Chnar HussamDr. Tola FARAJ

What is immunology?

• Immunology is the study of the immune system and is a very important branch of the medical and biological sciences. The immune system protects us from infection through various lines of defense.

• Immunology = study/ science of an organism of immune system.

What is an immunologist?

• An immunologist is a scientist and/or clinician who specializes in immunology.

Immune system

The immune system is a host defense system comprising many biological structures and processes within an organism that protects against disease.

IMMUNITY

immunity is the balanced state of multicellular organisms having adequate biological defenses to fight infection, disease, or other unwanted biological invasion, while having adequate tolerance to avoid allergy, and autoimmune diseases.

There are two type of immunity response:-

Innate immunity and adaptive immunity.

Innate immunity & adaptive Immunity

Blood Basics

Blood is a specialized body fluid. It has four main components: plasma, red blood cells, white blood cells, and platelets.

The Components of Blood

Blood cell formation from differentiation of hematopoietic stem cells in red bone marrow.

Red blood cells (RBCs)

Red blood cells (RBCs), also referred to as red blood c or erythrocytes are the most common type of blood cell and the vertebrate's principal means of delivering oxygen (O2) to the body tissues—via blood flow through the circulatory system The cytoplasm of erythrocytes is rich in hemoglobin, an iron-containing biomolecule that can bind oxygen and is responsible for the red color of the cells and the blood. In humans, mature red blood cells are flexible and oval biconcave disks. They lack a cell nucleus and most organelles, in order to accommodate maximum space for hemoglobin.

Human blood smear under 100X light microscope

White blood cells (WBCs)

• White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produce from the bone marrow Leukocytes are found throughout the body, including the blood and lymphatic system.

• All white blood cells have nuclei, which distinguishes them from the other blood cells, the anucleate red blood cells (RBCs) and platelets. The different white blood cell types are classified by structure (granulocytes or agranulocytes)

Neutrophils are the first responders to the infection

Their shape changes into amoeboid once when they are activated so they can extend their pseudopodia to attack invaders.

These are the smallest of all granulocytes with a characteristic multi-lobed nucleus with 3-5 lobes joined by a slender strand of genetic material.

Neutrophils

cytoplasm of the neutrophils has a large number of purple-colored granules, primary granules that have microbicidal activity.

i. These cells also secrete a range of proteins that have antimicrobial effects as well as tissue remodeling potential.

ii. Neutrophils have a short lifespan and thus destroy themselves during the degradation of foreign invaders. New neutrophils are then produced continuously in the bone marrow.

iii. Neutrophils are the most abundant granulocytes that makeup about 40% of white blood cells and 60% of the immune cells in the blood.

Eosinophils are granulocytes with a bilobed nucleus that can be differentiated from other leukocytes based on the presence of abundant large, acidophilic specific granules typically staining pink or red.

Eosinophils are relatively less numerous than neutrophils, constituting only 1%-4% of total leukocytes.

Eosinophils also modulate inflammatory responses by releasing chemokines, cytokines, and lipid mediators, with an important role in the inflammatory response triggered by allergies.

Basophils are also 12-15 μm in diameter but make up less than 1% of circulating

leukocytes and are therefore are difficult to find in normal blood smears.

Basophils contain large cytoplasmic granules which obscure the cell nucleus under the microscope when stained

when unstained, the nucleus is visible and it usually has two lobes.

Lymphocytes are round cells that contain a single, large round nucleus. There are two main classes of lymphocytic cells; the B cells that mature in the bone marrow, and the T cells that mature in the thymus gland.

The activated B cells, also known as plasma cells, produce highly specific antibodies that bind to the agent that triggered the immune response.

T cells, called helper T cells, secrete chemicals that recruit other immune cells and help coordinate their

attack.

Monocytes are a type of leukocyte, or white blood cell. They are the largest type WBC differentiate into macrophages and myeloid lineage dendritic cells

Monocytes are the largest white blood cell, measuring between 12 to 20 µm in diameter, approximately twice the size of red blood cells. In the peripheral blood, monocytes are typically easy to identify by their relatively large size and convoluted bilobed nuclei, often described as kidney-shaped

Platelets

Platelets, also called thrombocytes are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby initiating a blood clot. Platelets have no cell nucleus; they are fragments of cytoplasm that are derived from the bone marrow, which then enter the circulation. On a stained blood smear, platelets appear as dark purple spots

Blood smear showing the platelets

What is a blood smear?

A blood smear is a blood test used to look for abnormalities in blood cells. The three main blood cells that the test focuses

• red cells, which carry oxygen throughout your body

• white cells, which help your body fight infections and other inflammatory diseases

• platelets, which are important for blood clotting

on are:

• The most common technique of blood smear preparation is called the “wedge or push” technique. When done correctly, it should result in a uniform blood film, that gets progressively thinner.

• Giemsa stain is used to obtain differential white blood cell counts. It is composed from:-

• eosin are acidic dye which variably stains the basic components of the cells like the cytoplasm, granules etc.

• Methylene blue acts as the basic dye, which stains the acidic components, especially the nucleus of the cell.

Staining Procedure:-

• A thin film of the specimen on a microscope slide is fixed in pure methanol for 30 seconds, by immersing it or by putting a few drops of methanol on the slide. The slide is immersed in a freshly prepared 5% Giemsa stain solution for 20–30 minutes (in emergencies 5–10 minutes in 10% solution can be used), then flushed with tap water and left to dry.

Blood smear under microscope in different magnification