1. White bloods cell

• Thymus — a gland between the lungs and just below the neck.
• Spleen — an organ that filters the blood. It sits in the upper left of the abdomen.
• Bone marrow — found in the center of the bones, it also produces red blood cells.
• Lymph nodes —small glands positioned throughout the body, linked by lymphatic vessels.

Phagocytes:

• Neutrophils — these are the most common type of phagocyte and tend to attack bacteria.
• Monocytes — these are the largest type and have several roles.
• Macrophages — these patrol for pathogens and also remove dead and dying cells.
• Mast cells — they have many jobs, including helping to heal wounds and defend against pathogens.

Lymphocytes:

• B lymphocytes - they produce antibodies and help alert the T lymphocytes.

• T lymphocytes - they destroy compromised cells in the body and help alert other

2. Skin: most powerful immune system of human body is skin. It is the first level protection from foriegn bodies