B-Lymphocytes
The majority of mature B cells develop into plasma cells upon activation, whose task is to produce antibodies against foreign substances. Antibodies are Y-shaped proteins that can bind to very specific structures, so-called antigens. These are mostly proteins, but often also sugars (carbohydrates) or lipids (fatty molecules).
The antibodies are also called immunoglobulins and are divided into 5 classes based on their structure and function (IgG, IgM, IgD, IgA and IgE). The antibodies now help in various ways to fight the infection: Toxins such as the tetanus toxin can be neutralized or the entire pathogen can be labeled. A pathogen marked in this way can now be absorbed and digested by certain defense cells, the macrophages and neutrophil granulocytes.
However, the pathogen can also be destroyed and dissolved by natural killer cells, as well as macrophages and granulocytes by substances that are toxic to the pathogen. Some antibodies can also clump together the target cells to make them easier to detect and more receptive. Another way is through activation of the complement system, which is composed of several unspecific proteins that dissolve labeled cells in a kind of chain reaction. However, these proteins are permanently present in the blood in comparable concentrations and are part of the innate immune system. In addition, antibodies also activate mast cells, which release pro-inflammatory substances such as histamine, which increase the blood supply to the affected tissue and thus make it easier for other defense cells to reach the site of inflammation.
T lymphocytes
There are two main groups of T-lymphocytes, the T-helper cells and the T-killer cells, as well as the regulatory T-cells and again long-lived T-memory cells. The T-helper cells enhance the effect of the other defence cells by binding to antigens presented on other defence cells and then releasing cytokines, a kind of attractant and activator for other defence cells. Here again there are further specialized subgroups depending on the type of defense cells required.
They play a special role in the activation of plasma cells and T-killer cells. T-killer cells are also called cytotoxic T-lymphocytes because, in contrast to most defense cells, they destroy their own cells instead of those foreign to the body. This is always necessary when a body cell is attacked by a virus or other cell parasite or when a cell is altered to such an extent that it could become a cancer cell.
The T-killer cell can attach itself to certain antigen fragments that the infected cell carries on its surface and kill them by different mechanisms. A particularly well-known example is the introduction of a pore protein, the perforin, into the cell membrane. This causes water to flow into the target cell, whereupon it bursts.However, they can also induce the affected cell to destroy itself in a controlled manner.
Regulatory T-cells have an inhibitory function on the other defence cells and thus ensure that the immune reaction does not continue to escalate and can quickly subside again. They also play a major role in pregnancy, as they ensure that the cells of the fetus, which are also foreign to the body, are not attacked. T-memory cells, like the B-memory cells, are retained for a long time and also ensure a faster immune response when the pathogen reappears.
