CD-Cells-Immunity

Assessing the immune status is crucial, especially in cases of suspected viral, bacterial, or chronic infections as well as immunodeficiencies. The analysis of cellular immune defense through CD3+/CD56+/CD57+ NK cells provides important insights into the current health status. Similarly, determining CD19+ B-lymphocytes allows for a detailed view of the humoral immune system. These two parameters offer valuable information about the immune system and assist in the diagnosis and treatment of various diseases. The following sections will explain the functions and significance of these cells and their clinical relevance in more detail.

Lymphocytes develop from precursor cells located in the bone marrow. B cells originate from the bone marrow and natural killer (NK) cells migrate directly to the periphery from there. T cells, however, migrate from the bone marrow to the thymus, where they undergo positive and negative selection. They develop into naive T cells, which have not yet encountered antigens, and patrol between blood and lymphatic tissues. Natural killer T cells are another T-cell lineage that develops in the thymus and has a receptor, in addition to the T-cell receptor, that recognizes glycolipid antigens of bacterial origin.

T cells (CD3+ lymphocytes) recognize antigens by means of their T cell receptor and the cofactor CD3 and induce or regulate the innate immune defense. T cells are increased in viral (e.g. rubella) and bacterial (in the overcoming phase) infections as well as fungal infections (e.g. pneumocystis, candida), typhoid, T-cell leukemia and lymphomas and in smokers. Reduced T-cells are found in congenital (DiGeorge syndrome, SCID, Wiskott-Aldrich syndrome, Ataxia teleangiektasia/LouisBar syndrome) and acquired (malignant diseases, infectious diseases, e.g. AIDS, tuberculosis), immune defects, after radiation and medication with immunsuppressants (e.g. e.g. glucocorticoids), cytostatics or steroids, in chronic liver diseases (e.g. liver cirrhosis, alcohol-related and non-alcohol-related steatohepatitis, hepatitis C), burns, SLE and other autoimmune diseases, Cushing's syndrome, renal failure and iron deficiency anemia.

Role of T cells (CD3+ lymphocytes) and NK cells (CD3-CD16+/CD56+/CD57+) in the immune system and their clinical significance.

T cells (CD3+ lymphocytes) recognize antigens through their T-cell receptor and the co-factor CD3, inducing or regulating cellular immune responses. Elevated T cells are observed in viral (e.g., rubella) and bacterial (during recovery phase) infections, as well as fungal infections (e.g., Pneumocystis, Candida), typhoid fever, T-cell leukemias, and lymphomas, as well as in smokers. Reduced T cells are found in congenital (DiGeorge syndrome, SCID, Wiskott-Aldrich syndrome, Ataxia telangiectasia/Louis-Bar syndrome) and acquired (malignant diseases, infectious diseases, e.g., AIDS, tuberculosis) immunodeficiencies, following radiation exposure, and medication with immunosuppressants (e.g., glucocorticoids), cytostatics, or steroids, in chronic liver diseases (e.g., liver cirrhosis, alcohol-related and non-alcohol-related steatohepatitis, hepatitis C), burns, SLE, and other autoimmune diseases, Cushing's syndrome, renal insufficiency, and iron deficiency anemia.

Natural killer cells (NK cells, CD3+/CD16+/CD56+/CD57+) are effector cells of the innate immune system. They kill tumor cells and virus-infected body cells by inducing their apoptosis. Elevated NK cells are observed in viral infections, mycoplasma infections, or after drug-related immune stimulation, as well as in NK cell leukemia (rare). Decreased NK cells are found in progressive tumor growth, in smokers, during physical exercise, and during a low-calorie diet.

CD57+ cells, which belong to NK cells, can be reduced in chronic bacterial intracellular infections such as Borrelia, Mycoplasma, or Chlamydia.

B-lymphocytes are essential in specific immune responses. In this process, B lymphocytes control the antibody-based defence response of the body.

Via immunoglobulins (Ig) on the cell surface, B lymphocytes can recognize specific antigens. These antigens are proteins foreign to the body.

In addition to immunoglobulins, B lymphocytes have other markers on the membrane surface that are used to identify subtypes of B cells (lymphocyte differentiation). The most common surface markers of B lymphocytes are CD19, CD20 and CD21.

Structure and regulation of CD19 expression

CD19 as a 95-kDa member of the immunoglobulin super-family expressed exclusively on B lymphocytes is classified as a type I transmembrane protein, with a single transmembrane domain with a cytoplasmic C-terminus, and extracellular N-terminus. CD19 is a critical co-receptor for B cell antigen receptor (BCR) signal transduction. The surface density of CD19 is highly regulated throughout B cell development and maturation, until the loss of expression during terminal plasma cell differentiation. CD19 expression in mature B cells are 3-fold higher than that found in immature B cells, with slightly higher expression in B1 cells than in B2 (conventional B) cells.

CD19 as a marker for the humoral immune response

B cells (CD19 lymphocytes) are a subgroup of lymphocytes and can be measured quantitatively in the blood as part of leukocyte typing (determination of immune status). The B cells fulfil their function within the framework of the so-called humoral immune system (production of antibodies).

The importance of the CD19 marker is that it allows analysis of B lymphocytes, which are responsible for humoral immune responses.

CD19 is one of the most reliable surface biomarkers for B lymphocytes they have an important role in the normal expansion and function of the peripheral B-cell pool. It contributes to maintaining the balance between humoral, antigen-induced response and tolerance induction, as even small modulations in CD19 expression can impact B cell signalling thresholds and dramatically affect the sensitivity and specificity of B cell mediated immunity.

Interpretation of CD19 values in the context of B-cell functions

• High numbers of the absolute B-Cells CD19+ can be sign of general B-cell lymphocytes stimulation: current virus infection (EBV-Early Infection), recent infection with bacteria, autoimmune disease, lymphadenopathy.
• Low numbers of the absolute B-Cells CD19+ can be sign of general B-cell lymphocytopenia: cellular immunodeficiencies, stressful situations, therapies with cortisone or with B-cell depleting antibodies. Chemotherapies, radiation therapies, infections with pathogens that damage the immune system and higher levels of mycotoxins biomarkers can be the reason for low CD19.