Lecture 24 - Immune System

== Leukocytes ==
Leukocytes are white blood cells (5-10k/µL), which are much less numerous than red blood cells(~5M/µL). Leukocytes help fight against disease, and are the basis of the human immune system.
=== Granulocytes ===
Granulocytes, also known as polymorphonuclear leukocytes, have granules that are visible through a special staining technique. They include neutrophils, easinophils, and basophils.
==== Neutrophils ====
Neutrophils produce lysozymes, and make up 50-90% of the WBC count. It is the most common phagocytic leukocyte, and forms most of the pus that is expressed by the human body. Pus is made up of mostly dead microbes and neutrophils.
==== Eosinophils ====
Eosinophils make up 1-3% of the white blood cell count and also produce lysozyme. Their major function is to produce toxins against large, eukaryotic parasites. They are phagocytic for the Antigen-Antibody complex, which occurs as a result of an antibody binding to an antigen. Eosinophils, along with mast cells,  can lead to allergies.
==== Basophils ====
Basophils are rare and occupy less than 1% of the total white blood cell count. Their granules contain histamines and heparin. Histamines are vasodilators, and heparin is an anti-coagulant.
Mast cells are very similar to basophils, but are not considered a granulocyte. They are resident rather than wandering.
=== Agranulocytes ===
==== Monocytes ====
Monocytes make up 3-8% of the white blood cell count. They form dendritic cells, wandering macrophages, and fixed macrophages. 
Dendritic cells are phagocytic cells found in tissues. They engulf pathogens and present them to other WBCs
Wandering macrophages stay in the blood stream.
Fixed macrophages, also known as histiocytes, go into tissue specifically and protects the tissue from infections.
Dendritic cells and fixed macrophages are part of the reticuloendothelial system.
==== Lymphocytes ====
Lymphocytes make up 20-30% of the white blood cell count
B-lymphocytes contribute to antibody production and humoral immunity, and T-lymphocytes are involved on cell mediated immunity and antibody regulation. 
== Change in White Blood Cell Count ==
=== Increases ===
==== Leukocytosis ====
A general increase in WBC.
==== Neutrophilia ====
Occurs with pyogenic cocci such as Staph/Strep.
==== Eosinophilia ====
Caused by fungal infections
==== Lymphocytosis ====
A symptom of viral infections such as mononucleiosis.
=== Decreases ===
==== Leuko(cyto)penia ====
AIDS is the decrease in CD4 T-helper cells. 500-1000/µL is normal but any number under 200/µL would have AIDS. Usually it takes about 8 years for HIV to develop into AIDS.
Neutropenia
== Local Inflammation ==
Local inflammation is caused by vasodilators like histamines, which cause increased blood flow to the area. This increased blood flow leads to swelling (edema) caused by an increased permeability of blood vessels, heat, pain, and loss of normal function. 
Edema can be classified as serous (clear, recent wound, dilute toxins), purulent (pus formed by neutrophils), and fibrinogenic (clots).
== Antimicrobial Substances ==
Inflammation brings antimicrobial substances to the infected area such as complements and interferons.
Complements are a group of about 30 serum proteins that help fight infection by attaching to viruses and bacteria, helping an antibody recognize the foreign matter.
Interferons inhibit the expression of cancer genes and and are also antiviral. 
Type 1 interferons inculde Alpha (activate natural killer cells, a lymphocyte), beta (help in maturation of B- and T- Lymphocytes), Epsilon, and Omega.
The type 2 interferon is Gamma, and activates macrophages
The type 3 interferon is Lambda.
=== Lactoferrin and Transferrin ===
Lactoferrin and transferrin are proteins that bind to iron and prevents it from being oxidized. These proteins prevent bacteria from using the iron and therefore inhibits bacterial growth.
=== Lysozyme ===
== Acquired Resistance ==
Antibodies are very specific and will bind to specific pathogens after a host has been exposed to it. Its weaknesses include not having the antibody in the memory cells and mutations in the pathogen that changed how they interact with antibodies.