This blog is an introduction to a series of immunology assays that I learnt during an internship at a lab. These assays include Leishmann’s Staining, Peripheral Blood Mononuclear Cell (PBMC) isolation, Neutrophil Isolation, Enzyme-Linked Immunosorbent Assay (ELISA), and Ouchterlony Double Immunodiffusion (ODD).

Overview of the Immune System The immune system is a network of cells, tissues, organs, and proteins that protect the human body from pathogens, such as bacteria, viruses, and other microorganisms that cause disease. When a pathogen enters the body, it triggers an immune response. There are broadly two types of immune responses: innate and adaptive.

Innate immunity is present in every human from birth and is designed to eliminate pathogens in a non-specific or general manner. Since all pathogens are treated in the same way, this response is fast-acting and is considered the body’s first line of defense. Examples of innate immunity include the skin, mucous membranes, tears, stomach acid, saliva, and reflexes such as sneezing.

Adaptive immunity, on the other hand, is specific to the type of pathogen the body is trying to eliminate. Through active immunity, the body can also help prevent a second infection of the same type by remembering the specific pathogen that caused it. This response is carried out by specialized blood cells, including B and T lymphocytes.

Blood and Its Cellular Components Blood contains a plasma component, which is the yellow liquid portion of blood, and a cellular component. The cellular component includes red blood cells (erythrocytes), platelets, and white blood cells.

White blood cells can be further classified into granulocytes and agranulocytes, based on the presence or absence of granules in their cytoplasm. Granulocytes include neutrophils, eosinophils, and basophils. Agranulocytes include natural killer cells and lymphocytes, which consist of B cells and T cells.

Of these blood cells, granulocytes, B cells, T cells, and natural killer (NK) cells are crucial for immunity. In addition, cells such as dendritic cells and monocytes also play an important role in immune responses.

All blood cells are formed from cells called haemopoietic stem cells (HSCs). Stem cells are unspecialized cells that can replicate an unlimited number of times while also being able to differentiate into specialized cells of various types. HSCs are immature blood stem cells found in the bone marrow. They can differentiate into all types of blood cells and are therefore considered multipotent, meaning they can differentiate into a specific group of related cell types.