Ultrastructural and histochemical investigation of the terminal capillaries in the spleen of the carp (Cyprinus carpio L.)

Summary In the spleen of the carp arterial capillaries of a highly differentiated structure have been studied by light and electron microscopy. These capillaries share various structural characteristics with the sheathed capillaries (ellipsoids of Schweigger-Seidel) of higher vertebrates. The long arterial capillaries of the carp spleen are provided with cuboidal endothelial cells containing filaments approximately 7 nm in diameter. There is no basal lamina. The endothelial cells form various types of cell junctions, but there are also extensive areas without any junctions. Here, a free passage is possible between the capillary lumen and the subendothelial space. The capillaries possess a single-layered sheath of macrophages. Characteristically, the sheath macrophages possess long and slender cell processes forming a loose framework, the meshes of which are filled with lymphocytes and spindle cells. The sheath macrophages show a zone of ectoplasm rich in filaments. They also contain numerous phagolysosomes rich in hydrolytic enzymes, as identified histochemically. The sheath is sharply limited against the pulp by a thick layer of collagen fibers.     

On the endogenous peroxidase in the spleen of swine (author's transl)]

We studied the distribution of endogenous peroxidase in the spleen of swine by modifications of the Graham and Karnovsky diaminobenzidine procedure. There is a peroxidatic activity in the majority of the ellipsoid cells (cells of the sheathed capillaries of Schweigger-Seidel), which is localized in the endoplasmic reticulum and the perinuclear cisterna. This staining is inhibited completely by aminotriazole and is rapidly destroyed even by low concentratoins of glutaraldehyde. Furthermore, the reaction is abolished after boiling of tissue sections or in the absence of H2O2. The macrophages of the red pulp and a minority of the ellipsoid cells are peroxidase negative. Our results are discussed in respect to some recent studies on the system of mononuclear phagocytes. It is suggested, that the enzyme active ellipsoid cells represent a special form of macrophages, enzyme histochemically related to Kupffer cells and resident peritoneal macrophages. The enzyme negative cells of the ellipsoids are probably fibroblasts.     

Structure of the spleen of the sea bass (Dicentrarchus labrax): A light and electron microscopic study

The spleen of sea bass (Dicentrarchus labrax) is composed mainly of red pulp, whereas the white pulp is poorly developed. The red pulp consists of clear reticular cells intermingled with blood cells, sinusoids, and melanomacrophage centers (MMCs). The MMCs are enclosed by an interrupted connective tissue capsule and show some areas in continuity with the adjacent pulp. The MMCs are formed by the association of free macrophages that have phagocytosed some blood cells. Sparse white pulp is diffuse, forming a cuff around the pulp arteries and MMCs, or occurring in small groups between the splenic cords. A longitudinal artery and vein, lying side by side, extend the length of the spleen. Frequently the capillaries are surrounded by a sheath of macrophages or ellipsoids. These macrophages may contain erythrocytes in varying degrees of degradation. Lymphopoiesis and plasmapoiesis occur in the sparse lymphold areas. Abundant plasma cell groups may indicate the presence of antibody production.     

The origin of the follicular capillaries in the human spleen.

The major arteries which supply the follicular capillaries in the human spleen do not arise as they do in most mammals as lateral or radial branches from the central artery but come from penicillar arteries which penetrate the marginal zone and enter the follicle at various points around its circumference. Such arteries may have a very short course through the red pulp or they may pursue very long courses. Upon entering the follicle, these arteries branch a number of times, the branches remaining together in a tight array of parallel arterioles along with capillaries formed from them, the whole bundle being enveloped by a reticular fiber sheath. There is thus formed an arteriolar-capillary bundle. The whole bundle may branch. From the sides, especially from its central end, arterioles and capillaries radiate out to all parts of the follicle to terminate in the marginal zone or in the follicle itself.     

Selective binding of biotinylated albumin to the lymphoid microvasculature

Chemically modified albumin binds to the surface of microvascular endothelia lining the vessel wall in several tissues. In this paper, we report that following their biotinylation, ovalbumin (bioOVA) and bovine serum albumin (BSA) [biotinyated albumin (bioAlb)] showed heterogeneous binding to distinct vascular subsets in different lymphoid tissues. The binding of bioAlb could be demonstrated both by fluorescent and enzymohistochemical techniques. In the spleen, the reaction was restricted to the red pulp sinuses whereas the white pulp vessels (including the central arteriole) and the marginal sinus were negative for bioAlb binding. In lymph nodes, the strongest labeling was observed in the medullary sinuses. In the thymus, the most prominent labeling of capillaries was restricted to the corticomedullary area where it was found to be less intense compared with the splenic reaction. The splenic reactivity of bioAlb in the mouse was defined using antibodies against endothelial cell subsets in distinct vascular beds in the red pulp and marginal zone, respectively. The bioAlb-binding elements of the splenic red pulp sinus architecture corresponded to the display of hyaluronan receptor stabilin-2 and subset-specific marker IBL-9/2 while they differed from the expression pattern of both the complementary red pulp sinus subset and the marginal sinus-lining cells expressing MAdCAM-1 antigen, respectively. Similar red pulp sinus-restricted reactivity could be demonstrated in the human, rat, and guinea pig. The use of bioAlb may thus offer a reliable probe for the histological identification of select microvascular endothelia in lymphoid tissues.     

Studies of a primitive mammalian spleen, the opossum (Didelphis virginiana)

Light microscopic sections of the adult opossum (Didelphis virginiana) spleen were observed to lack venous sinuses; this primitive mammalian spleen may be classified as non-sinusal in nature. In the spleen of the opossum, the capillary segments of the penicillar arteries lacked ellipsoid sheaths characteristic of certain mammalian spleens. Separating the lymphoid nodules from the surrounding red pulp was a distinct band of vascular tissue, the marginal zone. Arising from the central artery within the lymphoid nodule, vessels of capillary dimension were observed to terminate within the marginal zone and the area between lymphoid nodule and marginal zone. In addition to the vascular channels established by the terminal arterial vessels within the red pulp, the system of vessels within the marginal zone has been implicated as an important intermediate vascular channel within the spleen.     

Microvascularization of the spleen in larval and adult Xenopus laevis: Histomorphology and scanning electron microscopy of vascular corrosion casts

Microvascular anatomy and histomorphology of larval and adult spleens of the Clawed Toad, Xenopus laevis were studied by light microscopy of paraplast embedded serial tissue sections and scanning electron microscopy (SEM) of vascular corrosion casts (VCCs). Histology showed i) that white and red pulp are present at the onset of metamorphic climax (stage 57) and ii) that splenic vessels penetrated deeply into the splenic parenchyma at the height of metamorphic climax (stage 64). Scanning electron microscopy of VCCs demonstrated gross arterial supply and venous drainage, splenic microvascular patterns as well as the structure of the interstitial (extravasal) spaces representing the “open circulation routes.” These spaces identified themselves as interconnected resin masses of two distinct forms, namely “broccoli‐shaped” forms and highly interconnected small resin structures. Arterial and venous trees were clearly identified, as were transitions from capillaries to interstitial spaces and from interstitial spaces to pulp venules. Venous sinuses were not diagnosed (nonsinusal spleen). The splenic circulation in Xenopus laevis is “open.” It is hypothesized that red blood cells circulate via splenic artery, central arteries, penicillar arteries, and red pulp capillaries primarily via “broccoli‐shaped” interstitial spaces, pulp venules and veins into subcapsular veins to splenic veins while lymphocytes circulate also via the interstitial spaces represented by the highly interconnected small resin structures in vascular corrosion casts. In physiological terms, the former most likely represent the fast route for blood circulation, while the latter represent the slow route. J. Morphol. 277:1559–1569, 2016. © 2016 Wiley Periodicals, Inc.     

Macrophages and Reticulum Cells in the Spleen of the Dogfish,Scyliorhinus canicula

The presence and ultrastructural features of reticulum cells and macrophages were studied in the spleen of the dogfish Scyliorhinus canicula. Three morphologically distinguishable regions of the spleen were identified: the white pulp, the red pulp and the ellipsoids. In all three, the splenic parenchyma was a meshwork supported by reticulum cells and fibres. Reticulum cells in both the white and the red pulp are irregular elements, the processes of which are joined by cell junctions and embrace developing reticular fibres. The ellipsoids of the dogfish spleen are terminal branches of the splenic arteries of the white pulp, with a sheath consisting of reticulum cells, reticular fibres, ground substance, macrophages and occasional lymphocytes. Isolated melanomacrophages also occur in the ellipsoid walls as well as in the red pulp. In both the white and the red pulp phagocytic reticulum cells, and macrophages appear frequently forming cell associations with surrounding blood cells, mainly lymphocytes. The functional significance of the ellipsoids and the cell-cell clusters of the white and the red pulp is discussed in relation to the immune capacities demonstrated in elasmobranchs.     

B lymphocyte compartments in the human splenic red pulp: capillary sheaths and periarteriolar regions

The microvasculature of human spleens is still incompletely understood. Two enigmatic types of red pulp microvessels, penicillar arterioles and sheathed capillaries, have already been described in the nineteenth century without gaining much attention afterwards. We performed a detailed analysis of sheathed capillaries to clarify the cellular composition of their sheaths by immunohistological double-staining experiments. Capillary sheaths comprise three different cell types, namely specialized cuboidal CD271⁺⁺ inner sheath cells surrounded by CD271^? macrophages and accumulations of B lymphocytes. The CD271⁺⁺ inner sheath cells express the chemokine CXCL13 in a unique single dot pattern. Sheath-associated B lymphocytes consist of IgM⁺, IgD⁺⁺, and of “switched” cells. T lymphocytes do not accumulate in pericapillary sheaths. The predominant sheath-associated macrophage population is CD163^?CD68⁺ and thus differs from the majority of red pulp macrophages. The sheath-associated macrophages strongly express CD169 only in perifollicular sheaths, but not in sheaths located deeper in the red pulp. IgM⁺, IgD⁺⁺, and “switched” B cells are also closely associated with red pulp arterioles characterized by the expression of smooth muscle actin in muscle cells and in branched periarteriolar stromal cells. Capillary sheaths are observed in a post-arteriolar position and appear to be of limited length. We suggest to change the term “Vagina periarteriolaris makrophagocytica” of the international histological and embryological terminologies to “Vagina pericapillaris.”     

The argentophil reticular cells of the mammalian spleen. II. The argentophil reticular cell arrangement inside the red pulp and its relationship with the endothelial lining cells of the splenic sinuses

The red pulp's argentophil reticular cell network of the spleen is composed by 3 types of fixed cells: 1. the primitive reticular cell, slightly argentophil; 2. the small reticular cell; 3. the larger reticular cell, strongly argentophil and phagocytic. This latter shows the classical morphological characteristics attributed to the reticular cells of the spleen. The large argentophil reticular cell may become free, constituting a 4th cell type, the free macrophage. A 5th reticular cell type is the dendritic cell found into the lymphatic follicles of the white pulp. The argentophil reticular cells of the red pulp assemble together to form the reticular cells' network, that occurs inside the red pulp cords. The primitive and the small reticular cell form the fundamental network on which the large cells are apposed. The reticular cells of this network maitain relationship with the arterial terminal vessels of the red pulp, being responsible by the ellipsoid structure. In those arteriolar segments without ellipsoid and in those mammalian species devoid of ellipsoid, the white pulp reticular cells, that surround the blood vessel as a part of the lymphoid periarteriolar sheath, mix with the red pulp's reticular cells and both can hardly be discriminated. The ellipsoids are formed by large argentophil cells arranged in concentrical layers around its lumen that sometimes appear devoid of endothelial lining cells. The red pulp's argentophil reticular cells, either the small or the large ones, contributed to the structure of the splenic sinuses' wall; its thin processes surround the sinus wall outside the endothelial lining cell as fibrillar structures that cross the back side of the lining cells. Two or more argentophil reticular cells send fibrillar processes to a single sinus. The perisinusal reticular cells may send a process between adjacent endothelial lining, cells that insinuate and attain the sinus lumen; this process becomes thick and eventually, the reticular cell enter the sinus lumen as a free macrophage. The argentophil reticular cells of the red pulp make connection between the capsule or the trabeculae and the reticular cell network. The endothelial lining cells of the splenic sinuses are not argentophil.     

The equine spleen: an electron microscopic analysis

The capacity of the equine spleen to store and rapidly release as much as half the circulating blood volume after adrenergic stimulation depends upon the size of the spleen, its muscular capsule, and the distinctive structure of its red pulp. The unit, or lobule, of red pulp is a cylinder of pulp spaces organized in a reticular meshwork, supplied by a peripheral ring of arterial capillaries, and drained by a central venule. Reticular cells, which make up the meshwork of the pulp, contain an extraordinarily large complement of microfilaments and intermediate filaments and are richly innervated by nerves containing both dense and lucent core vesicles typical of adrenergic nerves. The wall of the pulp venule contains large apertures. The capacious red pulp would thus appear capable both of large-scale blood storage and, by the contractile adrenergic innervated reticulum and open venous vasculature, of rapid expression of stored blood into the circulation. Antigen-presenting cells are present not only in B and T cell zones in white pulp but in the periarterial macrophage sheath of red pulp as well. The periarterial macrophage sheath is one of the first sites of antigen capture, and the presence of these cells confers on it an immunological role.     

Microcirculatory pathways in normal human spleen, demonstrated by scanning electron microscopy of corrosion casts

Confusion regarding microcirculatory pathways in normal human spleen has arisen due to extrapolation from pathological material and from other mammalian spleens, not to mention difficulties in tracing intricate three-dimensional routes from the study of thin sections or cut surfaces of tissue. We examined microcirculatory pathways in normal human spleens freshly obtained from organ transplant donors. A modified corrosion casting procedure was used to obtain an open view of vessels and their connections. Our results demonstrate: 1) "arteriolar-capillary bundles" within lymphatic nodules and extensive branching of arterioles in the marginal zone (MZ); 2) the marginal sinus around lymphatic nodules; 3) the peri-marginal cavernous sinus (PMCS) outside the MZ or immediately adjacent to the nodule itself; the PMCS receives flow via ellipsoid sheaths and MZ, or directly from arterial capillaries, and drains into venous sinuses; 4) fast pathways for flow into venous sinuses via ellipsoid sheaths; 5) arterial capillary terminations in the reticular meshwork of the red pulp or MZ ("open" circulation); direct connections to venous sinuses also occur ("closed" circulation), although rarely; and 6) numerous open-ended venous sinuses in the MZ, allowing a large proportion of the splenic inflow to bypass the red cell filtration sites in the reticular meshwork and at venous sinus walls.     

α- and β-receptor control of catecholamine secretion from isolated adrenal medulla cells

Summary The structural characteristics and cellular elements of the boundary zone between the white and red pulp of the human spleen were studied by SEM and TEM. The boundary zone consisted of both the perifollicular region and the region surrounding the periarterial lymphoid sheath. The perifollicular region was further subdivided into two, equally thick layers. The inner half layer of the perifollicular region outside the mantle zone of the lymph follicle was composed of tightly packed medium-sized lymphocytes, interspersed by a small number of reticular cells. The outer half layer was composed of a reticular cell meshwork containing blood cells in vessels, which communicated with the splenic cords of the red pulp. Intermittent rows of reticular cells distinguished the outer from the inner half layer. The region surrounding the periarterial lymphoid sheath revealed the same type of reticular cell meshwork as the outer half layer of the perifollicular region. Capillary ends opened into the reticular cell meshwork, which suggested the presence of an open circulation in the human spleen. A deep lymphatic vessel which communicated with the periarterial lymphoid sheath was noted.     

Thymic and splenic changes following injection of living Brucella and BCG in the Guinea pig

Summary The thymic and splenic reactions, following injections of BCG and living Brucella M. in the guinea pigs, were studied. Both microorganisms injected intravenously produced thymic involution, maximal after BCG inoculation, followed by regeneration that was complete by day 10 in Brucella M.-treated guinea pigs, and by day 15, in BCG injected guinea pigs. Increase of mitotic index was more accentuated and more persistent after Brucella M. than after BCG treatment in the thymus. After a short involution period the spleen of injected animals increased in size in both groups. The splenic enlargement was dramatic and occurred at an accelerated rate in animals given BCG. It appeared to be the result of a conspicuous involvement of the red pulp by multiple granulomas. In Brucella M. treated guinea pigs the splenic enlargement was less obvious, but the splenic white pulp was more abundant in BCG-treated guinea pigs. Granulomas were observed only in the periarterial sheaths of the white pulp.These observations provide evidence for the hypothesis that injections of both BCG and Brucella M. provoke a proliferation of B and T lymphocytes, a migration of T lymphocytes from the thymus to the T-dependent area of the spleen which seems, perhaps, more marked after injection of Brucella M., and a strong granulomatous histiocytic reaction which is more conspicuous in animals given BCG.     

Über die Peroxidase in der Schweinemilz

Zusammenfassung Die Verteilung von Peroxidase-Aktivitäten in der Milz des Hausschweines wurde mit verschiedenen Modifikationen der Diaminobenzidin-Methode nach Graham und Karnovsky untersucht. Der größere Teil der Hülsenzellen der Schweigger-Seidelschen Kapillarhülsen besitzt Peroxidase-Aktivität im endoplasmatischen Reticulum und im perinukleären Raum. In den Makrophagen der roten Pulpa und in einem kleineren Teil der Hülsenzellen war diese Enzymaktivität nicht nachzuweisen. Die Befunde werden mit den bekannten enzymhistochemischen Eigenschaften der Makrophagen des Systems mononukleärer Phagozyten verglichen. Die Stellung der peroxidasepositiven Hülsenzellen im System mononukleärer Phagozyten wird diskutiert.

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On the endogenous peroxidase in the spleen of swine

Summary We studied the distribution of endogenous peroxidase in the spleen of swine by modifications of the Graham and Karnovsky diaminobenzidine procedure. There is a peroxidatic activity in the majority of the ellipsoid cells (cells of the sheathed capillaries of Schweigger-Seidel), which is localized in the endoplasmic reticulum and the perinuclear cisterna. This staining is inhibited completely by aminotriazole and is rapidly destroyed even by low concentrations of glutaraldehyde. Furthermore, the reaction is abolished after boiling of tissue sections or in the absence of H₂O₂. The macrophages of the red pulp and a minority of the ellipsoid cells are peroxidase negative. Our results are discussed in respect to some recent studies on the system of mononuclear phagocytes. It is suggested, that the enzyme active ellipsoid cells represent a special form of macrophages, enzyme histochemically related to Kupffer cells and resident peritoneal macrophages. The enzyme negative cells of the ellipsoids are probably fibroblasts.

     

Distribution of extracellular matrix proteins type I collagen, type IV collagen, fibronectin, and laminin in mouse folliculogenesis

The extracellular matrix (ECM) plays a prominent role in ovarian function by participating in processes such as cell migration, proliferation, growth, and development. Although some of these signaling processes have been characterized in the mouse, the relative quantity and distribution of ECM proteins within developing follicles of the ovary have not been characterized. This study uses immunohistochemistry and real-time PCR to characterize the ECM components type I collagen, type IV collagen, fibronectin, and laminin in the mouse ovary according to follicle stage and cellular compartment. Collagen I was present throughout the ovary, with higher concentrations in the ovarian surface epithelium and follicular compartments. Collagen IV was abundant in the theca cell compartment with low-level expression in the stroma and granulosa cells. The distribution of collagen was consistent throughout follicle maturation. Fibronectin staining in the stroma and theca cell compartment increased throughout follicle development, while staining in the granulosa cell compartment decreased. Heavy staining was also observed in the follicular fluid of antral follicles. Laminin was localized primarily to the theca cell compartment, with a defined ring at the exterior of the follicular granulosa cells marking the basement membrane. Low levels of laminin were also apparent in the stroma and granulosa cell compartment. Taken together, the ECM content of the mouse ovary changes during follicular development and reveals a distinct spatial and temporal pattern. This understanding of ECM composition and distribution can be used in the basic studies of ECM function during follicle development, and could aid in the development of in vitro systems for follicle growth.     

Specific localization of epidermal-type fatty acid binding protein in dendritic cells of splenic white pulp

Dendritic cells in the splenic white pulp of mice were intensely immunoreactive for epidermal-type fatty acid binding protein (E-FABP). This specific immunostaining revealed a clear difference in morphology between the dendritic cells in the periarterial lymphoid sheath (PALS) and follicular dendritic cells in the follicles in terms of cell sizes and process branching. No immunoreactivity was detected in dendritic cells in the marginal zones and the red pulp, although endothelial cells of almost all capillaries in the red pulp were immunoreactive for E-FABP. After peritoneal injection of lipopolysaccharide, the immunoreactive cells in PALS progressively enlarged and became rounded in shape with a peak in size at 24 h postinjection and they eventually resumed the dendritic form at 48 h postinjection. Within each of the enlarged immunoreactive cell perikarya were included small immunonegative apoptotic cells, presumptive lymphocytes. Taken together, E-FABP is useful as a marker for dendritic cells in the splenic white pulp, and may be involved through combination with fatty acids in antigen presentation and retention as well as in cytokine production.     

Production and characterization of a monoclonal antibody to human type III collagen

Human type III collagen from placenta was isolated and purified for use as an immunogen. A monoclonal antibody was produced which specifically recognizes epitopes unique to type III collagen. The specificity of the antibody was determined by inhibition ELISA, an immunoblot assay, and by immunoprecipitation. Results indicated that the monoclonal antibody recognized only the alpha 1(III) polypeptide chains and did not crossreact with type I, IV, or V collagen. The monoclonal antibody was also used for immunohistochemical localization of type III collagen in tissue sections of human placenta, bovine spleen, and lymph node. In placenta, both large and small blood vessels showed pronounced staining of the tunica media, which contains largely smooth muscle cells, known to synthesize type III collagen. In contrast, the intimal areas and endothelial cells showed no staining with the antibody. In the placental villi, staining was limited to the villous core, where fine fibrillar structures showed strong staining. In lymph nodes, the capsule and pericapsular adipose cells were surrounded by a covering of type III collagen. Within the parenchyma of the node, staining was localized to a branching, reticular array of fine fibers. In the spleen, staining was pronounced in the capsule, splenic trabeculae, and white pulp, where blood vessel staining was especially prominent. The red pulp and splenic sinuses contain little or no type III collagen. The fine network-like or reticular staining pattern found in the lymph node parenchyma is consistent with the staining pattern of the protein reticulin, and suggests that type III collagen may be closely associated with reticulin in certain tissues. Since the role of type III in tissues is unclear, this reagent will be useful in providing new information in this regard.     

Denervation does not change the ratio of collagen I and collagen III mRNA in the extracellular matrix of muscle

Denervation or inactivity is known to decrease the mass and alter the phenotype of muscle and the mechanics of tendon. It has been proposed that a shift in the collagen of the extracellular matrix (ECM) of the muscle, increasing type III and decreasing type I collagen, may be partially responsible for the observed changes. We directly investigated this hypothesis using quantitative real-time PCR on muscles and tendons that had been denervated for 5 wk. Five weeks of denervation resulted in a 2.91-fold increase in collagen concentration but no change in the content of collagen in the muscle, whereas in the tendon there was no change in either the concentration or content of collagen. The expression of collagen I, collagen III, and lysyl oxidase mRNA in the ECM of muscle decreased (76 +/- 1.6%, 73 +/- 2.3%, and 83 +/- 3.2%, respectively) after 5 wk of denervation. Staining with picrosirius red confirmed the earlier observation of a change in staining color from red to green. Taken with the observed equivalent decreases in collagen I and III mRNA, this suggests that there was a change in orientation of the ECM of muscle becoming more aligned with the axis of the muscle fibers and no change in collagen type. The change in collagen orientation may serve to protect the smaller muscle fibers from damage by increasing the stiffness of the ECM and may partly explain why the region of the tendon closest to the muscle becomes stiffer after inactivity.     

Pathology of the spleen in hepatosplenic schistosomiasis. Morphometric evaluation and extracellular matrix changes

Histological, ultrastructural, morphometric and immunohistochemical data obtained from the study of spleens removed by splenectomy from 34 patients with advanced hepatosplenic schistosomiasis revealed that the main alterations were congestive dilatation of the venous sinuses and diffuse thickening of the splenic cords. Splenic cord thickening was due to an increase of its matrix components, especially type IV collagen and laminin, with the conspicuous absence of interstitial collagens, either of type I or type III. Deposition of interstitial collagens (types I and III) occurred in scattered, small focal areas of the red pulp, but in the outside of the walls of the venous sinuses, in lymph follicles, marginal zone, in the vicinity of fibrous trabeculae and in sidero-sclerotic nodules. However, fibrosis was not a prominent change in schistosomal splenomegaly and thus the designation "fibro-congestive splenomegaly" seems inadequate. Lymph follicles exhibited variable degrees of atrophy, hyperplasia and fibrous replacement, sometimes all of them seen in different follicles of the same spleen and even in the same examined section. Changes in white pulp did not seem to greatly contribute to increasing spleen size and weight, when compared to the much more significant red pulp enlargement.