When the human being becomes ill, the internal fight against the external organisms that produce the disease begins: the immune system kicks in . There is a wide variety of responses to defend against attack, although in general we can speak of innate immunity and acquired immunity.
Innate immunity consists of a set of rapid defenses to a wide spectrum of microorganisms: the skin or mucous membranes are an example of this type of response, which also includes other internal defenses such as phagocytic cells, which are capable of ‘eating’ some attackers, or the inflammatory response.
Acquired immunity: spinning fine
Acquired immunity, by contrast, consists of slower responses to specific microorganisms. It could be said that, while innate immunity is a much more ‘beastly’ response, in acquired immunity it is spun finer and the defenses are directed directly to the specific external agent. It develops only after being in contact with them: they are defenses that can very specifically distinguish inducing agents. This recognition is achieved by white blood cells called lymphocytes, which produce two general types of immune responses: humoral and cell-mediated.
In the humoral response, B lymphocytes secrete defense proteins called antibodies. Also known as immunoglobulins (Ig), antibodies are glycoproteins that circulate in the blood to seek and capture antigens that damage the body. Once found, they join them and mark them for recognition and removal.
There are several types of immunoglobulins depending on their molecular structure and their functions: IgM, IgG, IgA, IgE and IgD. In recent times, and due to the serological tests developed to detect the presence of antibodies in the blood specific to SARS-CoV-2, there is a lot of talk about IgG and IgM. IgMs are the first class of immunoglobulin produced after initial exposure to antigen, and their concentration in the blood declines as infection progresses. IgGs appear later, but they are also the most abundant in the blood. Furthermore, they are the only class of immunoglobulin that crosses the placenta, thus conferring passive immunity to the fetus. They are thought to be related to immune memory, so their presence in the blood may indicate possible immunity to the specific infectious agent.
Vaccine development
The power of antibody specificity and antigen-antibody binding has been exploited in laboratory research, in clinical diagnosis, and in the treatment of disease. It has also led to vaccines, which make the body anticipate a possible contagion by making it immune.
The antibodies, once produced, remain circulating in the blood for months, generating immunity for long periods to a certain antigen. This was the basis of the first vaccines: to create this immunity to certain external pathogens after causing the segregation by the immune system of the corresponding immunoglobulins.
Source: Campbell & Reece, “Biology.” Seventh edition. 2007. Editorial Médica Panamericana
