Overview
This lecture reviews the innate (nonspecific) immune system and introduces the adaptive (specific) immune system, focusing on B lymphocytes and the humoral immune response.
Nonspecific (Innate) Immune System
- The innate immune system acts as the body's first and second line of defense against pathogens.
- First line barriers include skin, stomach acid, and acidic skin oils, preventing pathogen entry.
- Second line defenses include inflammatory responses and phagocytes that attack any foreign invaders.
- Nonspecific means these defenses do not target specific pathogens; they respond to anything unfamiliar.
- Phagocytes such as dendritic cells, macrophages, and neutrophils are all white blood cells (leukocytes).
Specific (Adaptive) Immune System
- The adaptive immune system targets specific pathogens based on prior exposure.
- Main actors are lymphocytes, a type of leukocyte (white blood cell).
- Lymphocytes are divided into B lymphocytes (B cells) and T lymphocytes (T cells).
- B cells mature in the bone marrow; T cells mature in the thymus.
- Adaptive immunity is unique to more advanced organisms (e.g., humans).
B Lymphocytes and the Humoral Response
- B lymphocytes participate in the humoral response, which targets pathogens in bodily fluids.
- The term "humoral" refers to the fluids (blood, lymph) where pathogens float before infecting cells.
- The humoral response is effective against viruses and bacteria not yet inside cells.
- Helper T cells can enhance the humoral response (to be covered in later lectures).
T Lymphocytes and Cell-Mediated Response (Preview)
- T lymphocytes participate in the cell-mediated response, targeting infected cells directly.
- Types of T cells include helper T cells and cytotoxic T cells.
Key Terms & Definitions
- Innate Immune System — First, nonspecific defense mechanism against pathogens.
- Phagocyte — White blood cell that engulfs and digests pathogens.
- Leukocyte — General term for white blood cells.
- Lymphocyte — Subclass of white blood cells (includes B and T cells).
- B Lymphocyte (B cell) — Lymphocyte matured in bone marrow; key in humoral response.
- T Lymphocyte (T cell) — Lymphocyte matured in thymus; key in cell-mediated response.
- Humoral Response — Immune defense targeting pathogens in body fluids.
- Cell-Mediated Response — Immune defense targeting infected body cells.
Action Items / Next Steps
- Review the differences between nonspecific and specific immunity.
- Prepare to study the roles and mechanisms of T lymphocytes in the next lecture.