The document provides an overview of the immune system, including: - Innate immunity acts as the first line of defense through barriers like skin and mucous membranes. Adaptive immunity responds later with targeted responses. - Adaptive immunity includes humoral immunity from B cells producing antibodies and cellular immunity from T cells killing infected cells. - Lymphocytes circulate and are concentrated in lymphoid tissues like lymph nodes and spleen to scan for pathogens using antigen presenting cells. Memory lymphocytes provide faster responses upon reexposure.

1. Immunology for the non-immunologist

2. Introduction to the Immune System

14. Properties of Adaptive Immune Responses

24. Cells of immune system

35. Tissue of Immune System