12th Grade

Beginning
First line: Physical and chemical barriers like skin, mucus, and stomach acid.

Second line: Innate immune responses such as inflammation, fever, and phagocytic cells.

Third line: Adaptive immunity involving lymphocytes (B cells and T cells) that target specific pathogens.

The nine main types of leukocytes and their roles are:

Neutrophils: Engulf and destroy bacteria.

Eosinophils: Attack parasites and respond to allergies.

Basophils: Release histamine in allergic reactions.

Monocytes: Develop into macrophages to engulf pathogens.

Macrophages: Large phagocytes that digest pathogens and present antigens.

Dendritic cells: Process antigens and activate T cells.

Natural Killer (NK) cells: Destroy virus-infected and cancer cells.

B lymphocytes (B cells): Produce antibodies for specific pathogens.

T lymphocytes (T cells): Include helper T cells that coordinate immunity and cytotoxic T cells that kill infected cells.