Learning Module 3 Lymphoid System Learning component 1 Basic Responses and Normal Histology

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1 Learning Module 3 Lymphoid System Learning component 1 Basic Responses and Normal Histology 1

2 Normal Bursa of Fabricius (BF) A. Normal Bursa showing a plical fold with numerous lymphoid follicles. B. Higher magnification of A show the epithelium beneath which are lymphoid follicles with an outer cortex and inner medulla. Note the relatively small amount of interfollicular connective (interstitial) tissue. C. Higher magnification of a bursal lymphoid follicle. D. Shows the region of specialized epithelium that has pinocytotic properties and is closely associated with an underlying follicle. 2

3 Thymus Normal A. Normal Thymus showing outer cortex and inner medulla. B. Normal thymus. C. Higher magnification of B shows the cortex and a small portion of medulla (bottom enter). D. Normal thymus higher magnification of B. 3

4 Thymus Normal and Atrophy A. Normal thymus. B. Thymus with severe atrophy. C. Normal thymus higher magnification of A. D. Atrophic thymus higher magnification of B. 4

5 Spleen Normal A. Normal spleen arrow identifies a bursa-dependent lymphoid follicle that is composed of B-lymphocytes. B. Higher magnification of A showing the well-demarcated bursa-dependent follicle. C. Higher magnification of A shows the periarteriolar lymphoid sheath (PALS). This is a population of T-lymphocytes. D. Higher magnification of A shows sheathed capillaries or ellipsoid sheaths (*) that are surrounded by reticular and dendritic cells. Lymphocytes in this region are B-lymphocytes. 5

6 Harderian Gland A. Low power saggital section of head shows the eye (E) and Harderian gland (arrow). B. Normal Harderian gland. C. Higher magnification of B shows the expanded interstitial tissue with a normal population of plasma cells and lymphocytes. D. Higher magnification of C shows numerous plasma cells. 6

7 Lymphoid Tissue: CALT, BALT, and Other Examples A. Conjunctival-associated lymphoid tissue (CALT) normal. B. Lymphoid follicle or nodular collection of lymphocytes in tracheal mucosa. Normal. C. Bronchial-associated lymphoid tissue (BALT). Normal. D. Lymphoid tissue in Meckel's diverticulum. Arrow shows a cyst that is not normal. This amount of lymphoid tissue is probably excessive or hyperplastic, but is not disease specific. 7

8 Conjunctival Associated Lymphoid Tissue (CALT) A. Eyelid with surface epithelium (E) and CALT (arrow). Conjunctival epithelium (CE) and tarsal plate (*) are shown. B. Higher magnification of A shows CALT that is normal. C. Higher magnification of B shos a bursa-dependent follicle. D. Higher magnification of B shows a diffuse collection of lymphocytes within the CALT. 8

9 Normal Lymphoid Tissue A. Shows a normal nodular and diffuses accumulation of lymphocytes at the esophageal proventricular junction. Epithelium of the esophagus (E) and an esophageal mucous gland (*) are shown. Arrow identifies a bursadependent or nodular collection of lymphocytes. B. Higher magnification of A at arrow shows the bursa-dependent follicle. Normal. C. Bone marrow with a nodular collection of lymphocytes normal finding. D. Higher magnification of C shows the normal nodular collection of lymphocytes. 9

10 Apoptosis in Thymus and BF A. Thymus with many apoptotic cells. A pyknotic nucleus is shown (arrow). This is normal or programmed cell death defined as apoptosis and is expected to be seen in lymphoid organs. B. Higher magnification of A shows pyknotic nucleus (arrow). The pattern of apoptosis in lymphoid organs create the starry sky appearance. C. Apoptosis in the medulla (arrow) of a bursal follicle is normal. D. Many apoptotic cells are shown in this higher magnification of C with a pyknotic nucleus (arrow) identified. 10

11 Necrosis and Atrophy: Lesion Scores 1 4 A. Bursa Fabricius of 7-day old broiler is considered normal and has an atrophy or lesion score of 1. B. This BF has a follicle with a cyst and increased interstitial space lesion score = 2. C. Multiple follicles are undergoing necrosis and atrophy lesion score = 3. D. Most of follicles have necrosis or atrophy lesion score = 4. 11

12 Reticular Hyperplasia Spleen A. Reticular tissue is prominent around the sheathed capillaries (box) and number of lymphocytes is decreased. B. Higher magnification of A shows relative loss of lymphocytes and increased pale staining reticular cells. C. Higher magnification of A (box) shows a sheathed capillary surrounded by large numbers of pale reticular cells. D. Reticular hyperplasia and/or loss of lymphocytes is shown. 12