Adaptative Immunity + Lymphoid Organs, Lymphocyte recirculation

Question 1

What are lymphocytes?

Answer 1

small cells, agranular cytoplasm and a large nucleus. 2 Types B and T produced in different regions. Told apart by antibodies present on the cell surface.

Question 2

What’s cluster differentiation?

Answer 2

nomenclature for cell surface molecules - discriminates between different blood cells, more than 350 CD markers. CD 3,4,8 on T cells.

Question 3

How many T cells per litre?

Answer 3

1.5 x 10^9 T cells per litre. In blood 7.5x10^9 (only 2% of total). All T lymphocytes express CD3. TCR - antigen specific receptor 90% of T cells have alphabeta ( ⅔ express marker CD4 , ⅓ cd8) - , 10% gamma.

Question 4

What’s a CD4 cell?

Answer 4

T helper cells, regulatory cells that secretes cytokines

Question 5

What’s a CD8 cell?

Answer 5

cytotoxic T cells - lyse infected cells and secrete cytokines

Question 6

How do T cells present Antigens?

Answer 6

T cells only recognise processed antigens that are present on the surface of another cell using a receptor. Antigen is presented using Major Histocompatability Complex

Question 7

What are B lymphocytes?

Answer 7

surface antigen receptor = immunoglobulin like molecule.
Dont express CD3,4,8.
They express CD19,20 + MHC Class II (can present antigen to helper T cells).
Function is to produce antibodies.

Question 8

Role of antigen presenting cells?

Answer 8

Antigen presenting cells present antigens (peptides) to T lymphocytes to initiate acquired immune response - i.e. dendritic cells, b lymphocytes and macrophages.

Question 9

What’s a Primary Lymphoid Organ?

Answer 9

Where lymphocytes are produced (Lymphopoiesis) - B (bone marrow)+T Lymphocytes - thymus but precursors come from the bone marrow (stem cell) - go into ciruclation to the thymus and mature

Question 10

What’s a Secondary Lymphoid Organ?

Answer 10

lymphocytes interact with antigens and other lymphocytes to generate immune response - spleen, lymph nodes, mucosal associated lymphoid tissues (MALT), GALT (gut), NALT (nasal).

Question 11

What happens to mature lymphocytes from the Thymus?

Answer 11

When T lymphocytes mature from primary organs they recirculate into the blood and secondary lymphoid tissues then back into the blood. Stop recirculating if they detect their antigen.

Question 12

What is the Thymus?

Answer 12

bilobed 5cm, below the thyroid in the thoracic cavity - packed full of proliferating lymphocytes.

Divided into lobules by septa(septum) each one has a dark staining region on the outside(cortex), medulla (middle), hassall’s corpuscles - whirls of fibroblasts that form regulatory T cells.

No obvious changes during infection - no increase in lymphocyte production.

Question 13

Thymus Function?

Answer 13

Function= development and maturation of lymphocytes. Thymic output of new lymphocytes decreases with increased age - less able to respond to completely new pathogens. TOtal number of T lymphocytes doesnt change, more are able to respond to former infections.

Question 14

What is the Bone Marrow?

Answer 14

B cell development (and red blood cells) - changes to the bone marrow during infection does occur - increased white cell production - more neutrophils. In foetus - all bones + liver/spleen produce cells. In adults - mainly flat bones - vertebrae, illiac bones, ribs

Question 15

Secondary Lymphoid Organs?

Answer 15

Lymphatic system - drainage system fluid collected from tissue cells is absorbed and filtered through lymph nodes. 2-3L returned back into blood (via superior vena cava), during infection antigen likely to enter lymph nodes that a phsycial repsopnse can be generated. In cancer - have cancer cells entered lymph nodes.

Question 16

What’s a lymph node?

Answer 16

afferent lymphatic vessels (into), one efferent (leaving) vessel, medulla in middle, outerside has lymphoid follicle (B cell aggregates), enlarged follicle = proliferating and differentiating B cell - ongoing response = germinal centre.

Phagocytes remove antigens present in the lymph. Fluid filtered through lymphocytes that they may encounter antigen and produce immune reponse.

Lymph nodes become enlarge = on-going immune reponse during infection. Supplied by blood artery and vein, thats how lymphocytes enter the lymph node in the first place - the lymphocytes leave circulation and enter lymph nodes when they encounter high endothelial venule (hev) - much thicker.

B cells move to the outside - follicle, and T cells towards the medulla - following chemokines (signals) by chemotaxis.

Question 17

Role of the spleen?

Answer 17

filter for antigens in the blood.
Two main areas - red pulp (RBCs) + white pulp (WBCs) (white circles).
Phagocytes scavenge in spleen and take up dead cells. Lymphocytes leave blood supply directly here.
White pulp is immediately surrounding blood vessels. Primary Follicle - B cell area, Periarterial Lymphatic Sheath (T cell area). Ongoing immune response = larger primary follicles = germinal centres.