CancerQuest | The Acquired Immune Response

Specific or adaptive immunity is the second line of defense because it is initiated if the non-specific, innate immune response is unable to completely combat the invading pathogen. The two systems really overlap somewhat. As an example, proteins produced by cells of the adaptive immune system are present in secretions like tears that also contain proteins that are part of the innate immune system.

The adaptive response develops and changes over the course of our lifetimes and is thus also called acquired immunity. The cells and proteins of the adaptive immune response are highly specific for invading pathogens or abnormal cells within the body. This is in contrast to the broad spectrum activities of the components of the innate immune system.

Like our innate immune system, the specific immune response is composed of several different types of cells and the proteins that they produce. The main cells of the adaptive immune response originate in our bone marrow and mature at different locations in the body. The cells may float around in the blood stream or lymphatic system or take up residence in an organ or tissue. Two of the main cell types spend a significant amount of time in the lymphatic system and are known as lymphocytes. These two types of immune cells are called T cells and B cells. A major protein component of the acquired immune system is the antibodies produced by B cells.⁽¹⁾

The specific immune response is an active system with four defining characteristics:

Antigen Specificity-The cells and proteins of this system only recognize very particular protein fragments (peptides) on other cells or dissolved in body fluids
Diversity in the number of peptides that can be recognized. The acquired immune system is capable of responding to an astounding number of different foreign proteins. The number of different proteins and organisms we encounter in our lifetime is enormous and the acquired immune system is able to generate a specific response against each one!
Memory-A hallmark of the acquired immune response is that if the same foreign object is encountered again, the response is both more rapid and more intense. The system remembers the things it has encountered. This is accomplished by the generation of 'memory' cells that live for a long time, waiting for their chance to re-activate and lead the charge.
Self:Non-Self Discrimination-The acquired immune system is able to recognize cells that have been altered in very minor ways and respond appropriately. An example of self:non-self discrimination is the rejection of an organ following transplantation. A kidney from one person may be recognized as 'non-self' by the recipient and destroyed. For this reason, transplant patients receive medications that lower their immune response.⁽¹⁾

Of importance to us: The genetic changes that make normal cells into cancer cells can also alter them in ways that can be detected by the immune system.