Heterogeneity of lymphocytes as central operating units of the immune system

Immune response is divided into natural and adaptive although such strict division is rather contentious as one type of immunity influences another one and vice-versa; moreover, there are cells and immune mechanisms, which stay somewhere in an interface. B and T lymphocytes represent principal cells of adaptive immunity. Not one of them form a uniform population. B cells comprise of three subpopulations (follicular, B1, marginal zone). Concerning T cells, the situation is more complicated. There are two basic populations, that expressing T cell receptors α, β and that expressing γ, δ receptors. T cells αβ are very heterogeneous; we can distinguish helper, cytotoxic and regulatory cells. Moreover, among T helper cell, are there seven subsets. Except the above-mentioned effector B and T cells, each group has its counterpart in the form of memory cells, wherein the memory T cell are of three types. The other group of lymphocytes represent so-called unconventional cells. NK, NKT a MAIT are their representatives; they are also heterogeneous. Ultimately, a novel group of cells appeared recently. It stays just on the interphase between natural and adaptive immunity. We know these cells under the name innate lymphoid cells (ILCs). They are also not uniform - three basic populations are well characterized: ILC1, ILC2, ILC3. Moreover, in the frame of each family, we can distinguish more subsets. Enumeration of said cell types indicates complexity and mutual interconnection of immune processes in order to maintain biological integrity of an individual.