Human Health and Disease — Part 2: Immunity and vaccines: visual lesson, CBSE Class 12 Biology

Lesson

Immunity

Part 2 — how the body defends itself, and how vaccines prepare it in advance.

In this lesson you will

Distinguish innate and acquired immunity, and active and passive immunity
Describe the structure of an antibody and the roles of B and T lymphocytes
Explain primary and secondary immune responses and how vaccines work
Explain allergies and autoimmunity and name the lymphoid organs

Concept

Innate immunity

Innate immunity is non-specific and present at birth. It consists of four kinds of barriers.

Table of the four barriers of innate immunity with examples
Barrier	Examples
Physical	Skin; mucus coating of the respiratory, gastrointestinal and urogenital tracts
Physiological	Acid in the stomach, saliva in the mouth, tears from the eyes
Cellular	Leucocytes: PMNL-neutrophils, monocytes and natural killer lymphocytes; macrophages, which engulf microbes
Cytokine	Interferons secreted by virus-infected cells protect non-infected cells

Concept

Acquired immunity

Acquired immunity is pathogen-specific and has memory. The first encounter gives a low-intensity primary response; a later encounter with the same pathogen gives a highly intensified secondary (anamnestic) response.

Table of the roles of B-lymphocytes, T-lymphocytes and memory cells
Cells	Role
B-lymphocytes	Produce antibodies into the blood: humoral (antibody-mediated) immunity
T-lymphocytes	Help B cells produce antibodies; carry out cell-mediated immunity (CMI), including graft rejection
Memory cells	Remember the pathogen, giving a faster, stronger secondary response

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