MLT 115 Mod 2 Les 1 pt 2
Overview of Lymphocytes
Discussion on different types of lymphocytes: T lymphocytes, B lymphocytes, and natural killer (NK) cells.
Lymphocyte Types
T lymphocytes and B lymphocytes: Key components of the adaptive immune system.
Natural Killer (NK) Cells:
Characteristics: Lack traditional T and B lymphocytes and CD3 marker
Function: Potent immune cells that focus on tumor cells and some bacteria; capable of actively killing cells.
Concerns: Rarely seen in excess; decreased or dysfunctional NK cells can lead to problems, such as in HIV infection. HIV = decreased helper T cells. NK cells are dysfunctional enough to attack the patient and not the HIV.
White Cell Antigens
White cells have antigens called HLA (Human Leukocyte Antigens)
Human Leukocyte Antigens (HLA):
Serve as identification markers on white blood cells, similar to blood typing antigens.
CD Markers:
Used to genotype and identify white blood cells at a molecular level.
CD3: Present in most lymphocytes but absent in NK cells.
B Lymphocytes
Maturation and Function:
B lymphocytes mature in the bone marrow and make up less than 15% of circulating lymphocytes.
Responsible for humoral immunity (antibody production).
It’s individually programmed to produce one specific antibody.
Process of Activation:
Upon stimulation, The B cell secretes the antigen and interleukins to transform it into a plasma cell, which is responsible for producing millions of antibodies.
Plasma cells reside in lymph nodes, spleen, and gut-associated lymphoid tissue and in the medullary cords of the lymph nodes.
Immune Response Dynamics
Primary Immune Response:
Naive T lymphocytes interact with antigen-presenting cells during the Lag phase.
Clonal expansion occurs, leading to production of antibodies by plasma cells during the Log Phase.
As immune response progresses, cells undergo apoptosis (programmed cell death) during the Decline.
Secondary Immune Response:
Memory B cells persist after the primary response and enable a quicker response upon re-exposure to the antigen.
Anamnestic response: Refers to the memory component of the immune response.
CD Markers and Cell Lineage
Importance of CD Markers:
CD means Cluster Differentiation
CD markers specify the lineage of lymphocytes and facilitate identification (e.g., T helper vs. T cytotoxic). They also all cell to cell interaction.
Lymphocyte identification through CD markers:
T helper cells: CD3+, CD4+, CD8-
T cytotoxic cells: CD3+, CD4-, CD8+
Regulatory T cells: CD4+, CD25+
NK cells: CD3-
B lymphocytes: Typically CD19+
Flow Cytometry:
Technique used to identify different cells based on the presence of CD markers.
Essential for assessing HIV patients and determining CD4/CD8 ratios, which are normally 2:1.
A CD4 count < 200 indicates progression to AIDS in HIV patients.
Human Leukocyte Antigen (HLA) System
HLA is also known as MHC (Major Histocompatibility Complex)
Major Histocompatibility Complex (MHC):
Gene products identifiable on white cells, crucial for organ transplantation compatibility.
Its molecule marks a cell as self encoded by a group of genes contained in a section of a specific chromosome.
A match of 4-6 antigens reduce risks of graft-versus-host disease (GVHD).
The 4-6 antigens are marked with HLA, a letter and a number
HLA Designation:
Example of HLA identified cells types for matching in transplants: Ms. Connie’s doctor stated that she will need Type O blood and as many of HLA 47 antigens as possible.
Inherited as haplotypes (one from each parent).
Neutrophils and Phagocytosis
Role of Segmented Neutrophils:
It’s main role is to perform phagocytosis, which is the process of engulfing and destroying bacteria.
Phagocytosis Process:
Four key steps:
Chemotaxis: Neutrophils and monocytes are attracted by chemicals towards bacteria.
Adherence: Binding to the bacteria.
Engulfment: Formation of pseudopods surrounding the bacteria, like a fake hug.
Lysosome Formation: a vacuole forms on the pseudopod that is surrounding the bacteria
Fusion: The bacteria becomes fused to the cell
Death and Destruction: Granules released phagozymes to cause lysis of the cell and the bacteria, like Kamikaze on the bacteria (I die, you die with me!)
Note:this entire process is critical and shall be memorized for exams.
Monocytes and Macrophages
Macrophages are grown up tissue monocytes
Monocyte and Macrophage Function: They clean up dead and worn out cells just like "garbage trucks". They also participate in antigen presentation.
Pus Formation: Occurs from dead neutrophils and monocytes.
Eosinophils and Basophils
Basophils and Mast Cells:
Mast cells are tissue basophils
They contain both histamine and heparin, which is released during allergic reactions.
Eosinophils:
They detect histamine release
Respond to histamine release by increasing in numbers and suppressing basophil activity.
They also destroy intestinal worms (e.g., roundworms, tapeworms).
Abnormal Lymphocyte Responses
If there is a problem with a T lymph where it will not present an antigen to the B Lymph and cause it to react, then we identify it with Flow Cytometry to know what kind of T Lymph it is, if it is a T Lymph. You cannot ID Natural Killer Cells with Flow Cytometry.
Responses to Viral Infections (e.g. Mononucleosis):
Reactive lymphocytes appear atypical, larger with an irregular shape, indicating an immune response to pathogens like Epstein-Barr virus.
Conclusion
Lymphocyte function is interconnected and crucial for the immune response.
Questions about immunity often highlight complexity and interactions between different cell types. The knowledge of these interactions is critical for understanding immune responses.