Immune system  (part 2) 

Dendritic cells (DC)

• are phagocytes in tissues that are in contact with the external environment; therefore, they are located mainly in the skin, nose, lungs, stomach, and intestines 

• named for their resemblance to neuronal dendrites, as both have many spine-like projections, but dendritic cells are in no way connected to the nervous system

 • serve as a link between the bodily tissues and the innate and adaptive immune systems, as they present antigen to T cells, one of the key cell types of the adaptive immune system   

CELLS OF INNATE AND ADAPTIVE IMMUNITY 

• Lymphoid Lineage 

             – Large lymphocytes (large granular lymphocytes)

                 • Natural killer (NK) cells (CD16, CD56)

                 • Innate immunity to viruses and other intracellular                                 pathogens

                 • Participate in antibody-dependent cell-mediated                                     cytotoxicity (ADCC) 

            – Small lymphocytes

                 • B cells (CD19) 

                 • T cells (CD3, CD4 or CD8)

                 • Adaptive immunity 

            – Lymphocytes refers to small lymphocytes 

Lymphocytes; B cells; T cells

• B cells & T cells carry receptor molecules that recognize specific targets

 • T cells recognize a “non-self” target, such as a pathogen, only after antigens (small fragments of the pathogen) have been processed and presented in combination with a “self” receptor called a major histocompatibility complex (MHC) molecule 

• There are two major subtypes of T cells: the killer T cell and the helper T cell

 • Killer T cells only recognize antigens coupled to Class I MHC molecules, while helper T cells only recognize antigens coupled to Class II MHC molecules 

• A third, minor subtype are the γδ T cells that recognize intact antigens that are not bound to MHC receptors 

• In contrast, the B cell antigen-specific receptor is an antibody molecule on the B cell surface, and recognizes whole pathogens without any need for antigen processing. Each lineage of B cell expresses a different antibody, so the complete set of B cell antigen receptors represent all the antibodies that the body can manufacture 

Lymphocytes

• Many types; important in both humoral and cell-mediated immunity

 • B-cells produce antibodies

 • T- cells 

        – Cytotoxic T cells 

        – Helper T cells 

• Memory cells 

A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates.^[1] Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic adaptive immunity), and B cells (for humoral, antibody-driven adaptive immunity).^[2][3] They are the main type of cell found in lymph, which prompted the name "lymphocyte".^[4] Lymphocytes make up between 18% and 42% of circulating white blood cells.

• Plasma Cell (in tissue) 

        – Fully differentiated B cells, secretes Ab

 • Natural Killer cells

        – Kills cells infected with certain viruses 

        – Both innate and adaptive

        – Antigen presentation   

Typical recognition markers for Lymphocytes

Comparison of T and B cells

T-cells                                                        

 • responsible for cell mediated immunity 

 • Life span is long 

 • Differentiate inside Thymus Gland

 • Absence of surface antibodies 

 • Transformed in small lymphocytes by antigens

 • secrete Lymphokines

 • sub population are Cytotoxic T, Helper cells and suppressor     cells.

 • stimulate phagocytes and B-cells into activity. 

B-cells 

 • responsible for Humoral immunity

 • Life span is short

 • Differentiate inside Bone Marrow 

 • Surface Antibodies present

 • Transformed to plasma cells by antigens 

 • secrete antibodies 

 • sub population are memory cells and plasma cells

 • B-cells or B-lymphocytes produce antibodies .  

THE CLUSTER OF DIFFERENTIATION (CD) 

• CD nomenclature established in 1982

            – 1 st International Workshop and Conference on Human Leukocyte Differentiation                 Antigens (HLDA) held in Paris

• protocol for identification and investigation of cell surface                   molecules 

• intended for classification of many monoclonal antibodies                  generated by different laboratories around the world against           epitopes  on the surface molecules of leukocytes

 • CD number assigned on basis of 1 cell surface molecule                 recognized by 2 specific m Ab 

cluster of differentiation

• The (cluster of designation) (often abbreviated as CD) is a protocol      used for the identification and investigation of cell surface                  molecules present on White blood cells 

• CD molecules can act in numerous ways, often acting as receptors     or ligands (the molecule that activates a receptor) important to the     cell

• A signal cascade is usually initiated, altering the behavior of the         cell

• Some CD proteins do not play a role in cell signaling, but have            other functions, such as cell adhesion

• CD for humans is numbered up to 350 most recently (as of 2009). •  If the molecule has not been well-characterized, or has only one        mAb, it is usually given the provisional indicator "w" (as in                 "CDw186")  

THE CLUSTER OF DIFFERENTIATION (CD)

• CD markers on leukocytes

        Granulocyte                          CD45+, CD15+ 

        Monocyte                              CD45+, CD14+ 

        T lymphocyte                        CD45+, CD3+ 

        T helper lymphocyte             CD45+, CD3+, CD4+

        T cytotoxic lymphocyte        CD45+, CD3+, CD8+ 

        B lymphocyte                       CD45+, CD19+ 

        Natural killer cell                 CD45+, CD16+, CD56+, CD3-  

Components of blood

COMPLETE BLOOD COUNT WITH 

 DIFFERENTIAL (CBC WITH DIFF)

                                                References Ranges

 Erythrocytes (RBC)               4.0 to 5.4 M/uL 

 Thrombocytes (Platelets)      145 to 400 K/uL 

 Leukocytes (WBC)               4.8 to 10.8 K/uL 

 Neutrophils                            40 to 74 % 

 Band neutrophils                      0 to 9

 Eosinophils                              0 to 6 

 Basophils                                 0 to 1 

 Lymphocytes                         15 to 47 

 Monocytes                               0 to 12

Other Blood Cells

• Megakaryocyte                                          

        – Platelet formation

        – Wound repair

 • Erythrocyte

        – Oxygen transport

LYMPHOCYTES, LYMPHOID TISSUES AND ORGANS

• Lymphocytes originate in bone marrow

 • Lymphoid tissues and organs

         – Primary 

                 • Development and maturation of lymphocytes

                 • Bone Marrow (B cells) and thymus gland (T cells)

         – Secondary 

                 • Mature lymphocytes meet pathogens 

                 • Spleen, adenoids, tonsils, appendix, lymph nodes,                               Peyer’s patches, mucosa-associated lymphoid tissue                          (MALT) 

THE LYMPHATIC SYSTEM

• Lymph

         – Fluid and cells in lymphatic vessels 

• Lymphatic vessels

         – Collect and return interstitial fluid to blood

         – Transport immune cells throughout body 

         – Transport lipid from intestine to blood

 

• Lymph nodes 

         – Kidney shaped organs at intervals along lymphatic vessels

 • Other secondary lymphatic tissues and organs  

   

LYMPHOCYTES AND THE LYMPH NODES

• Naïve lymphocytes circulate between blood, lymph and secondary    lymph nodes 

• Pathogens from infected tissue sites are picked up by lymphatic       vessels and arrive at closest lymph node 

• T and B cells congregate at specific regions of nodes 

• Architecture and size of nodes change in response to activation of      lymphocytes       

LYMPHOCYTES AND THE SPLEEN

• Spleen 

        – Lymphoid organ in upper left abdomen 

        – Functions 

                • Remove damaged or old erythrocytes 

                     • Activation of lymphocytes from blood borne pathogens 

• Architecture of Spleen 

        – Red pulp 

                • Erythrocytes removed 

        – White pulp 

                • Lymphocytes stimulated  

SECONDARY LYMPHOID TISSUES ASSOCIATED WITH MUCOUS MEMBRANES

• Primary portals of entry for pathogens 

        – Respiratory tract

        – Gastrointestinal tract 

• Secondary lymphoid tissues 

        – Bronchial-associated lymphoid tissue (BALT) 

        – Gut-associated lymphoid tissues (GALT) 

                 • Tonsils, adenoids, appendix, Peyer’s patches 

• Pathogens are directly transferred across mucosa by “M” cells

Disclaimer:  
The content provided in this article is based on personal knowledge and educational background in the fields of health and nutrition. It is intended for informational purposes only and should not be considered a substitute for professional medical advice. For any health concerns, please consult a qualified healthcare provider .