Lymphocyte

The system may be a network of biological processes that protects an organism from diseases. It detects and responds to a good sort of pathogens, from viruses to parasitic worms, also as cancer cells and objects like wood splinters, distinguishing them from the organism's own healthy tissue. Many species have two major subsystems of the system. The innate system helps to provide a preconfigured response to various groups of stimuli and situations. The adaptive system provides a tailored response to every stimulus by learning to acknowledge molecules it's previously encountered. Thus the lymphocytes function is to provide the immune response.

Role of Lymphocytes

Lymphocyte, a sort of white blood corpuscle or leukocyte that's of fundamental importance within the system because lymphocytes are the cells that determine the specificity of the immune reaction to infectious microorganisms and other foreign substances. 

The leukocytes are further divided into three types:

1. Granulocytes

2. Monocytes

3. Lymphocytes

Hence leukocytes and lymphocytes are similar in function as they both work in order to protect our body. In human adults lymphocytes structure is roughly 20 to 40 percent of the entire number of white blood cells. They are found within the circulation and are also concentrated in central lymphoid organs and tissues, like the spleen, tonsils, and lymph nodes, where the initial immune reaction is likely to occur.

Types of Lymphocytes

The three major sorts of lymphocytes are T cells, B cells, and natural killer (NK) cells. Lymphocytes are often identified by their large nucleus.  These lymphocytes function to protect our body from pathogens by boosting our immune system.

T Cells and B Cells: 

T cells are also called thymus cells and B cells also called bone marrow or bursa derived. Thus for an adaptive immune response, these are the major components. T cells are responsible for cell-mediated immunity, whereas B cells primary importance is to provide humoral immunity. The function of these lymphocyte cells is to acknowledge specific "non-self" antigens, during a process referred to as antigen presentation. Once the invaders are identified, the cells generate certain specific responses that are built-in maximum to eliminate the specific pathogens or the cells that are infected by the pathogen. B cells answer pathogens by producing large quantities of antibodies which then neutralize foreign objects like bacteria and viruses. 

In response to pathogens some T cells, called T helper cells, produce cytokines that direct the immune reaction, while other T cells, called cytotoxic T cells, produce toxic granules that consist of powerful enzymes which induce the death of pathogen-infected cells. Following activation, B cells, and T cells these two types of lymphocytes are considered as the white blood cells of the immune system, they leave an enduring legacy of the antigens they need to be encountered, within the sort of memory cells. Throughout their lifetime of an animal, memory cells can "remember" each and every pathogen encountered and would show a strong and rapid response if the same pathogen is detected again; this is often referred to as immunity. 

Natural Killer Cells: 

NK cells are included in the innate immune system and they play a major role to protect the host from tumors and virally infected cells. These cells can review the functions of other cells as well, it includes macrophages and T cells. These killer cells belong to the family of cytokines and interferons, these are activated in order to fight against the infected cells. Activated killer cells release a kind of cytotoxic granules that are helpful to destroy the altered cells. These are named "natural killer cells'' because they do not require prior activation so as to kill cells that are missing MHC(Major histocompatibility class) class I.

X Lymphocyte: 

The X lymphocyte is a cell type that expresses two types of lymphocytes both a B-cell receptor and T-cell receptor and is hypothesized to be implicated in type 1 diabetes. Its existence as a cell type has been challenged thanks to irreproducibility at multiple institutions.

Structure of Lymphocytes

The blood lymphocyte is spherical in shape and the diameter measures approximately 5 μm as visualized by transmission microscopy. The nucleus has an abundance of condensed electron-dense, structure called heterochromatin, a feature characteristic of nonproliferating cells. The nuclei are approximately 0.5 to 1.4 μm in diameter. They are composed of three distinct and concentrically arranged structural units: the central region or agranular zone; the center, fibrillar region; and therefore the granular zone, which contains internuclear chromatin. The nuclear membrane consists of nuclear pores and a perinuclear space. The lymphocytes can live for a week or some of them can live for some years. This is the average lifespan of lymphocytes.

The cytoplasmic organelles of the lymphocytes are the characteristic feature of eukaryotic cells. Some organelles, just like the Golgi zone, are poorly developed. The cytoplasm is made up of free ribosomes and strands of the rough-surfaced endoplasmic reticulum. Centrioles, mitochondria, microtubules, and microfilaments are present within the cytoplasm adjacent to the cell wall. The cytoplasm also contains lysosomes, which are approximately 0.4 μm in diameter, are electron opaque and contain classic lysosomal enzymes. The lymphocyte plasma membrane contains the colloidal iron that helps in the formation of sialic acid. Lymphocyte cell membranes and cell coat glycoproteins are highlighted with other electron-dense markers, including phosphotungstic acid, lanthanum colloid, and ruthenium red.

[Image: lymphocytes diagram]