Adaptive immune system–Unlike the innate immune system described below, cells of the adaptive immune system (T cells and B cells) are relatively slow to be recruited to a site of infection…more on the order of days to weeks. These cells are much more adept at seeing a specific strain of bacteria and adapting so that it is more efficient at eliminating that bacteria. The adaptive immune system is also responsible for generating “memory”. This is why you generally won’t be sickened by chicken pox more than once. The cells of the adaptive immune system remember this virus the second time it’s encountered and is able to eliminate the infection before symptoms occur.
Antibodies–These are molecules made by B cells (of the Adaptive Immune system) that help to “neutralize” bacteria and viruses and block these pathogens from entering into your cells. They are very specific for particular viruses or bacteria and are important in protecting you from infection either after vaccination or after an initial infection. Antibodies are used a lot in the science world as tools to detect certain cells and proteins made by those cells. Techniques such as Western blotting, flow cytometry, and Immunofluorescence use antibodies.
B cells–B cells are part of the adaptive immune system. They are responsible for making antibodies described above that can neutralize bacteria and viruses, preventing them from gaining access to our cells. Since they are in the adaptive immune system, B cells are able to make small changes in their antibodies so that they are more specific for a virus or bacteria and therefore more efficient at eliminating the pathogen. B cells can also become “memory” B cells meaning they can stick around for very long periods so that if we are reinfected with a previously seen virus or bacteria, we won’t get quite as sick.
Cytokines–These are basically small proteins released from various cell types that communicate a message to a receiving cell. Examples of cytokines include Interferons, Tumor Necrosis Factor (TNF), and Interleukins.
Dendritic cells–-These cells are kind of the middle man between the innate (very early, nonspecific immune response) and adaptive (slower, very specific immune response). Like macrophages they also live in tissues, but unlike most macrophages, dendritic cells have the ability to take “evidence” of an infection from the infected tissue to a lymph node where they will come into contact with cells of the adaptive immune system (B cells and T cells). Cytokines and cell surface receptors are very important in their ability to communicate with these other cells.
Innate immune system–The innate immune system is a group of cells that work together to combat infection and injury very quickly. These cells (including monocytes, neutrophils, macrophages, basophils, etc.) are recruited within minutes to hours of infection or injury occurring. These cells recognize and are stimulated by very broad patterns that all bacteria or all viruses have, called Pathogen Associated Molecular Patterns or PAMPs. They are very good at starting inflammation and recruiting other immune cells including those of the adaptive immune system.
Macrophages–These are the big eaters that oftentimes live in tissues. They have a lot of roles including clean up. For instance when tissue damage occurs or when cells die because of a virus or any other cause, macrophages get rid of the mess basically by eating it. They are also important in using cytokines (see above) to either mobilize or halt other immune cells into action.
Pathogen Associated Molecular Patterns–Also called PAMPs. These are molecules found on broad categories of viruses or bacteria. These are the features that allow cells of the innate immune system to sense danger. They include things like components of the cell wall of bacteria (like lipopolysaccharide or LPS) and versions of DNA or RNA that aren’t found in human cells. They are the red flags that notify innate immune cells of danger.
Pattern Recognition Receptors–Also called PRRs. These are molecules on innate immune cells that detect the red flags of danger (PAMPs described above). They include things like the Toll-like receptors or TLRs and RIG-I like receptors. When innate cells recognize danger (PAMPs) using their PRRs they start a cascade of events necessary to get rid of the pathogen.
T cells–T cells are part of the adaptive immune system. They come in two forms, CD4+ and CD8+. CD4+ help B cells and macrophages and lots of other cells to be better at their job. CD8+ T cells are also called cytotoxic T cells and are very good at killing their target cells (usually a tumor cell or virally infected cell). T cells are “activated” into action with the help of a T cell Receptor that is very specific for cells infected with different types of viruses and bacteria. Like antibodies, T cell receptors can change during infection so that they are more specific for the infecting pathogen. And like B cells, T cells can become memory T cells and stick around for long periods in case of reinfection.