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Introduction to Lymph Node

I have found a note that I have made during a lymphoma talk at Sabah by Dr Ahmad Toha.  Here is the gist of it.

 About Lymphoid Follicles

There are two types of lymphoid follicles: one is primary and another is secondary lymphoid follicle.
Primary lymphoid follicle: dark blue in colour, stain less with Ki-67 proliferative index marker.
Secondary lymphoid follicle: has paler areas, stain more with Ki-67 proliferative index marker.

Useful markers for lymph nodes:
CD20: germinal centre and mantle cell.
CD79a: stronger staining at the mantle zone.
BCL-2: an anti-apoptotic marker, mostly stain outside the follicle with 'sprinkle' of positive cells inside the follicle.  These positive cells inside the follicles are T-helper cells.
CD21: identify the nodular appearance of the follicles.
Ki-67
BCL-6: germinal centre
CD10: germinal centre
IgD: stain outside the germinal centre (?mantle zone)

About Thymus:

1. Paracortex

Densely cellular
Located beneath cortex, at corticomedullary junction.
Composed of lymphoid cells and postcapillary venules.  These lymphoid cells are either small or large, depending on various stages of its development.
Interdigitating dendritic cells are present at this area.  These cells will present antigen to the lymphoid cells.  When there is increased dendritic cells, it will present as a 'mottled' pale area.

2. Medulla

Loss of CD20 surface markers.
Kappa to lambda ratio 2:1

3. Maturation of T cells within the thymus

Progenitor T cells (CD34, CD7 positive) --> Thymus cortex (CD2, CD7, CD34 positive) -->
Thymic medulla (CD2, CD3, CD7)

CD4:CD8 = 4:1

4. Lymphatic sinus

Found at subcapsular, medullary and cortical.

5. Postcapillary venules: found at paracortex.


About follicular hyperplasia and paracortical hyperplasia pattern: useful immunohistochemical stains:

Follicular pattern:
CD20
CD79a
CD3
CD5
BCL-2
BCL-6
CD10
Ki-67

Paracortical pattern:
CD20
CD3
BCL-2
CD30
Ki-67
CD68
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