Development of T and B cell areas in peripheral lymphoid organs of the rat

The lymph node revisited: development, morphology, functioning, and role in triggering primary immune responses

Scenarios have been proposed to explain how lymphoid components of a lymph node favor the encounter of a drained antigen with a circulating competent naïve lymphocyte to trigger a primary immune response. However, these scenarios rest on incorrect concepts about the organ. This situation resulted from a loss of interest for studies on in vivo lymphoid organs due to a widespread switch, decades ago, to work on suspended lymphoid cells. However, an in vivo holistic study of the organ continued in our laboratory. The present review synthesizes resulting knowledge on lymph node morphology and global functioning. We show that the opening of an afferent lymphatic vessel into the subcapsular sinus is the focal point from which the related portion of a lymph node-a node compartment-is developed. As to the formation of a compartment's lymphoid components, it is neonatally orchestrated by the dichotomic nature and distribution of antigens in this subcapsular sinus, which determines a dichotomic recruitment of circulating cells and the compartment's architectural complexity. The transport process of an antigen from a given tissue territory into restricted sites of the draining compartment further defines its local morphological features and activities, while providing the possibility to reduce the wandering of a short-lived naïve cell through innumerable target-devoid sites. We also explain that the nodal lymphoid components are not implicated in the triggering of primary responses, but are rather products of such responses. Scenarios for the triggering of primary responses, consistent with real node morphology and functioning, are proposed.

Fetal and early post-natal development of the human spleen: from primordial arterial B cell lobules to a non-segmented organ

Immunohistological analysis of 31 human spleens from the 11th week of gestation to the early postnatal period suggested that fetal organ development may be preliminarily divided into four stages. At stage 0 the organ anlage contained erythrocyte precursors, few macrophages and almost no lymphocytes. Fetal spleens of stage I exhibited arterial vascular lobules and lymphocytes just began colonizing the organ. At stage II, B and T lymphocytes formed periarteriolar clusters. B cell clusters predominated, because B cells aggregated around the more peripheral branches of splenic arterioles, while T cells occupied the more centrally located parts of the vessels. The vascular lobules of stage I and II consisted of central arterioles surrounded by B cells, capillaries and peripheral venules. The lobular architecture slowly dissolved at late stage II when sinuses grew out from the peripheral venules into the centre of the lobule. Interestingly, the B cell accumulations around peripheral arterioles did not represent the precursors of follicles, but apparently persisted as periarteriolar B cell clusters in the adult splenic red pulp, while follicles containing FDCs developed at late stage II from B cells in direct contact to T cell clusters around larger arterial vessels. At stage III before birth the lobular architecture was no longer recognized. The chemokine CXCL13 was already present in vascular smooth muscle and adjacent stromal cells at stage I before B cells immigrated. CCL21, on the contrary, was only demonstrated in fibroblast-like cells supporting T cell clusters from stage II onwards.

Formation of lymph follicles and germinal centers in the somatic and mesenteric lymph nodes of growing mice during ontogenesis

We investigated the age-dependent changes that occur in the numbers of lymph follicles and germinal centers in various lymph nodes in BALB/C and ICR mice aged between four days and 16 to 18 weeks. Young adult BALB/C mice have a relatively small body size, compared to ICR mice at the same stage, where there is a relatively large body size. In BALB/C mice somatic (popliteal, brachial, axillary, inguinal, submandibular and deep cervical) and mesenteric lymph nodes were examined. In ICR mice only the somatic (popliteal, brachial and axillary) lymph nodes were examined. In both BALB/C and ICR mice, the primary follicles were apparent in most somatic nodes by the 6th postnatal day. Up to 28 days of age, the number of follicles per node increased, reaching different levels in nodes from different locations. Thereafter, in most of the somatic nodes in BALB/C mice the number of follicles increased only slightly, although there was a substantial increase in ICR mice, reaching a peak or a plateau at 8 or 12 weeks of age. In the mesenteric (ileocecal) nodes in BALB/C mice, the primary follicles first appeared at 10 to 12 days, then there was a linear increase until a plateau level was reached at 8 weeks of age. Germinal centers appeared in the mesenteric nodes at 28 days and increased rapidly in number thereafter. In most somatic nodes germinal centers were scarcely observable until 8 weeks of age. Based on our observations we have three suggestions. Firstly, in BALB/C mice there were two different patterns of age-dependent changes in the numbers of lymph follicles in the somatic and the mesenteric nodes during ontogenesis. These different patterns are probably due to variations in the magnitude of the exogenous antigen stimulatory effect. Secondly, it seems likely that the variations in the numbers of lymph follicles that are produced in somatic nodes at different locations during the first 28 days after birth relate to the dimensions of the body regions that are drained by that particular somatic node at that stage of development. Thirdly, in the relatively small BALB/C mice, the ontogenetic production of lymph follicles in a somatic node is mostly completed during the first four weeks of life, whereas in the relatively larger ICR mice, this process may continue until the young adult stage of 8 weeks.

Patterns of age-dependent changes in the numbers of lymph follicles and germinal centres in somatic and mesenteric lymph nodes in growing C57Bl/6 mice

The timing of the first appearance of lymph follicles and germinal centres in various lymph nodes, and the ways in which numbers of these and IgM-synthesising cells increase within the nodes, were investigated in male and female C57Bl/6N mice aged from 4 d to 16 wk. The lymphoid organs examined were the Peyer's patches, spleen, somatic (submandibular, deep cervical, brachial, axillary, inguinal and popliteal) and visceral (mesenteric and lumbar) lymph nodes. Primary follicles appeared in most somatic lymph nodes 6 d after birth. The number of follicles per node then increased rather sharply in larger lymph nodes and slowly in smaller nodes, up to 28 d of age, reaching a level which varied according to the location of the node. Thereafter, the number of follicles in the somatic lymph nodes increased only slightly to moderately, reaching a peak or plateau at 8-12 wk. In the mesenteric (ileocaecal) nodes, primary follicles first appeared at 12 d, then increased linearly during the suckling period and after weaning to reach a plateau at 8 wk of age. Germinal centres appeared in the submandibular and mesenteric nodes at 28 d and their numbers increased consistently in the latter, while remaining low in the former. The impact of possible 'natural' exogenous antigen stimulation of the various lymph nodes was estimated from the presence of IgM-synthesising cells and germinal centres. Differences between the patterns of age-dependent changes in the numbers of lymph follicles observed in the somatic and mesenteric lymph nodes during their ontogeny are discussed in relation to differences in the magnitude of the exogenous antigen stimulatory effect. We also found that the variations in the numbers of lymph follicles produced in somatic lymph nodes at different locations during the first 28 d after birth reflected differences in the dimensions of the body regions drained by a particular somatic lymph node at this stage of development.

Electron microscopic study on the effect of alternate-day hydrocortisone therapy on lymphocyte populations in rat spleen and lymph nodes

The ultrastructural effects of 400 mg/M2/day of hydrocortisone sc, given alternatively from day 7 through day 19, were studied on the lymphocyte populations in the white pulp of the spleen and in the cortex of the mesenteric lymph nodes of the immunologically immature rat. Results were consistent with both a direct lytic effect of hydrocortisone on small lymphocytes of the nodular cortex of the mesenteric lymph nodes and an indirect effect on small lymphocytes of the periarterial lymphatic sheath (PALS) of the spleen supplied via the thymus. In contrast, medium-sized lymphocytes in the PALS appeared to be unaffected by hydrocortisone, while medium-sized lymphocytes of the nodular cortex of the mesenteric lymph nodes exhibited a temporary depletion of cytoplasmic organelles. Hydrocortisone appeared to depress protein synthesis in these latter cells. The decrease in numbers of lymphoblasts and plasmablasts observed in the nodular cortex of the mesenteric lymph nodes and the white pulp of the spleen is consistent with hydrocortisone interference with proliferation and differentiation of activated B cells.

Identification of beta-adrenoceptors in rat lymph nodes and spleen: an autoradiographic study

The anatomical localization of beta 1 and beta 2-adrenoceptors was studied in rat lymphoid tissues by quantitative autoradiography using [125I]cyanopindolol as a ligand. In lymph nodes, a significant density of these receptors was found in the medullary cords and the interfollicular cortex, while only low densities were observed in the paracortex. No detectable binding appeared in the remaining areas. In the spleen, these receptors were mainly localized in the capsule, marginal zone of white pulp and red pulp, while the labelling over the white pulp was extremely low. The subtype beta 2 was predominant in both lymph nodes and spleen. The results suggest that beta-adrenoceptors are present in mature cells in lymphoid tissues and are probably not involved in homing mechanisms.

Effect of alternate-day hydrocortisone therapy on the immunologically immature rat. III: Changes in T- and B-cell areas in lymph nodes

The histologic effects of the alternate-day hydrocortisone therapy (400 mg/M2 from day 7 to day 19 after birth) were studied on the mesenteric lymph nodes of immunologically immature rats. In rats sacrificed 2 days following the cessation of therapy, depletion of lymphocytes of the thymus-independent area was apparent. Smaller lymphocytes were more susceptible to the effect of hydrocortisone than larger ones. The absence of primary follicles, normally present at this age, suggested a possible retardation in development of the immune system. B lymphocytes appeared to be the target of the direct lymphocytolytic effect of hydrocortisone. In rats sacrificed 23 days following the treatment, immunological maturity was achieved, indicating the reversibility of the hydrocortisone effect.

Effect of alternate-day hydrocortisone therapy on the immunologically immature rat. II: Changes in T- and B-cell areas in spleen

The histologic effect of 400 mg/M2/day of hydrocortisone, given alternatively from day 7 to day 19 after birth, was studied on the spleen of the immunologically immature rat. Two days after the cessation of treatment, the periarteriolar lymphatic sheaths were found to be largely depleted of small lymphocytes. Immunoperoxidase studies confirmed a depletion of T lymphocytes. The effects of hydrocortisone on the thymus seem to be more important than its direct lymphocytolytic effect in producing this splenic lesion. In contrast, no apparent change in the number of medium-sized B lymphocytes in the marginal zone was detected. Medium-sized B lymphocytes of the spleen, reported to be responsible for IgM synthesis, appeared to be subjected to a different mechanism of hydrocortisone action, other than lysis, resulting in a decrease in antibody production. Primary follicles were not seen in spleens of hydrocortisone-treated rats. Twenty-three days after treatment, spleens had a histologically normal appearance.

Parallel development of noradrenergic innervation and cellular compartmentation in the rat spleen

By combining neurochemical measurement of norepinephrine (NE) with double-label immunocytochemistry for tyrosine hydroxylase-positive (TH+) noradrenergic nerves and specific lymphoid markers, we have examined the developmental compartmentation of noradrenergic nerves in the rat spleen. TH+ nerve fibers were present in the white pulp of the spleen at birth, among surface IgM-positive (sIgM+) B lymphocytes at the outer border of the periarteriolar lymphatic sheath (PALS), distant from the central artery. During the first 7 days, noradrenergic innervation developed rapidly, forming plexuses of nerve fibers along the central artery and its branches, among T and B lymphocytes of the PALS, and along the developing marginal sinus where ED3+ macrophages accumulate. The splenic concentration of NE (per mg wet wt.) and 3-methoxy-4-hydroxy-phenetheleneglycol (MHPG), a NE metabolite, increased rapidly during this period, suggesting that NE is available and released from these nerves. From 7-14 days, the white pulp expanded to include an inner PALS, outer PALS, marginal sinus, and marginal zone; during this period, TH+ fibers arborized principally among T lymphocytes of the inner PALS and adjacent to macrophages along the marginal sinus. By 14 days of age, NE concentration reached adult levels, although the MHPG/NE ratio (an index of NE turnover) remained higher throughout development than in adulthood. Finally, from 14-28 days, the outer PALS expanded to include follicles containing sIgM+ B lymphocytes. At the earliest stages of follicular development, a parafollicular rim of noradrenergic fibers was present, providing occasional branches which arborized within the follicle. No further changes were observed in either noradrenergic innervation or cellular compartmentation after 28 days of age. These findings suggest that noradrenergic fibers are present in developing compartments of the spleen at the earliest stages of their development, providing norepinephrine for interaction with a variety of adrenoceptor-bearing lymphoid and nonlymphoid cells.

Postnatal development of the splenic white pulp in the golden hamster Mesocricetus auratus. I. The periarterial lymphoid sheath (PALS)

The histological organization of the periarterial lymphoid sheath (PALS) was studied during the postnatal life of the golden hamster Mesocricetus auratus with special interest in the cell components occurring in each of their regions. Our results suggest a role of the cell components defining the splenic microenvironment at each developmental stage in governing the developmental process. This process can be temporarily and histologically divide into three stages: 1. At birth, a few lymphocytes and lymphoblasts surrounding the central artery define primitive PALS. 2. A second period is determined on the 2nd day by the appearance of a marginal sinus which bounds the two splenic compartments, white and red pulp. The PALS increases circumferentially around the central artery defined by the pattern of reticular cells and fibres. 3. Between the 4th and 10th days, the PALS reaches its definitive organization, except for the absence of primary and secondary lymphoid follicles, defining an inner and outer region. The marginal zone appears on the 6th day.

Noradrenergic sympathetic innervation of the spleen: III. Development of innervation in the rat spleen

The ontogeny of noradrenergic innervation and its compartmental development were studied in the rat spleen using glyoxylic acid histofluorescence and high-performance liquid chromatography (HPLC). Noradrenergic nerves were present at birth in bundles adjacent to the splenic artery and vein. On days 1-3, fluorescent profiles largely were associated with the vasculature and with the perivascular zone. By day 6, these fibers formed increasingly elaborate and tortuous plexuses around the central arteries and their branches. By day 10, fibers were present along the marginal sinus and extended into the developing marginal zone. Between day 10 and day 13 the largest increase in norepinephrine (NE) levels (per mg protein) were noted, and the periarteriolar lymphatic sheath (PALS) achieved its adult form, with increased innervation of the parenchyma. In contrast, the venous/trabecular system developed relatively late. The first trabecular fibers were evident at day 10, and the capsule was not innervated until day 13. From 13 days to adulthood, there was a gradual refinement and extension of existing patterns with no change in NE levels as measured by HPLC (per mg protein), suggesting that the innervation was keeping pace with rapid increases in spleen growth. The pattern of growth and development for noradrenergic nerves in the PALS remarkably parallels changes in T cell compartmentation during this period. We propose that norepinephrine is available for interaction with T cells at the earliest stages of development and could play a role in such processes as lymphocyte packing and the onset of immunocompetence.

Immunocytochemical study on the immune complex and germinal center of synovial tissue of rheumatoid arthritis with special regard to complement and follicular dendritic cells

To analyze the immunological role of lymphoid germinal centers and follicular dendritic cells (FDC) in synovial tissue of rheumatoid arthritis (RA), we tried to detect the immune complex in germinal centers by light and electron microscopic immunocytochemistry with special emphasis on immunoglobulin, complement components, RA factor, and DRC-1 antigen. Immunoglobulins mainly distributed intercellularly in the germinal center in a lacy network pattern, and show partial intracytoplasmic localization in some germinal center lymphoid cells. Early complement components of classical pathway (C1q, C4, C3c, and C3d) and RA factor distributed lacily similarily to immunoglobulin, but intracytoplasmic positivity is never observed. These coexistent positive sites are identical to DRC-1 positive sites which are the surface of extended processes of FDC membrane. A similar finding is observed in primary follicles or lymphoid aggregates less often than germinal centers. These results indicate that some germinal centers trap the immune complex, including RA factor at least closely related with FDCs, and also RA factor is one of the triggers of antigen as well as developing germinal centers.

Distribution of different cell types within the rat thymus in the neonatal period of life

This study attempted to define reciprocal positions of cell types within the thymus. Random or non-random contacts between specific cell types were analyzed by means of graph theory. For analysis, thymus blocks were sectioned serially and, then, thymus cells were categorized into types, based on morphological criteria. The distribution of individual cell types within the cortex, cortico-medullary zone and medulla was presented in form of a map. In the analysis, three types of epithelial cell, characteristic of each thymus zone, macrophages, Langerhans-like cells and lymphocytes were found in non-random relations to one another. Moreover, characteristic groups of cells associated with one another were also demonstrated.

Lymphocyte proliferation in neonatally thymectomized rats

Autoradiography has been used to evaluate lymphocyte proliferation in the neonatally thymectomized rat in comparison with the normal animal. The data obtained show that the proliferative activity of lymphocytes is greatly increased in the thymus-dependent areas 4-6 weeks after thymectomy, whereas it is normal or slightly increased 3 months later. It seems plausible to assume that a thymus factor or chalones in situ produced by specific cells normally regulate the proliferation of thymus-derived cells. The increase of the proliferative activity accounts for the repopulation of the thymus-dependent areas, which are completely replenished in the older animals. Recirculation of the thymus cells is not confined to the thymus-dependent areas.

Ontogeny of Peyer's patches of the rat

The development of lymphoid and nonlymphoid cells in Peyer's patches (PP) of the rat was investigated using light microscopical methods (routine histological techniques, enzyme histochemistry and immunohistochemistry). In newborn rats PP were mainly populated by T lymphocytes and Ia-positive nonlymphoid cells, which most likely are interdigitating cells. At about 12 days after birth the B and T cells were localized in defined regions, the follicular (FA) and interfollicular area (IFA), respectively. Compartmentalization within the FA started about 14 days after birth. The first signs of the development of secondary follicles were seen from about 18 days onward. PP obtained their mature structure at about 4 weeks after birth. It is suggested that after PP had developed fully, cells having cytoplasmic IgA migrate via the high endothelial venules (HEV) to the lamina propria of the intestine; cIgM and IgG cells seem to develop locally within the FA.

Ontogenetic development of T- and B-lymphocytes and non-lymphoid cells in the white pulp of the rat spleen

The location and temporal appearance of the different classes of lymphocytes were investigated in the developing white pulp of the rat spleen. Additionally, indications were sought for the involvement of non-lymphoid cells in the localization of lymphocytes. The lymphocytes were demonstrated by their surface determinants (W3/13, IgM, IgG, IgA, Ia) in a two-step immunoperoxidase method; the non-lymphoid cells were characterized by immuno-enzyme-histochemical techniques. The results showed that 1) already at birth strongly Ia-positive cells are present in the T-cell area; 2) the marginal zone develops as a distinct compartment, independent of the PALS and follicles; 3) follicles are recognizable at day 14, the capacity to trap immune complexes on follicular dendritic cells occurring one week later. A possible relation between the development of the follicles and the differentiation of the follicular dendritic cell is discussed.

Development of bronchus associated lymphoid tissue (BALT) in the rat, with special reference to T- and B-cells

The development of bronchus associated lymphoid tissue was studied in normal rats, in serial sections, using both routine histological techniques and the two-step immuno-peroxidase method on cryostat sections for demonstration of T lymphocytes, IgM-, IgG- and IgA-bearing B lymphocytes and plasma cells, respectively. BALT first appears 4 days postpartum (p.p.) as a condensation of reticulum cells near a lymph vessel, between the main bronchus and the accompanying artery. Only a few lymphocytes are present at first. Vascularisation is considerable 8 days p.p. and includes high endothelial venules. Leucocytes are seen in transit in both blood- and lymph vessel walls. Lymphocytes populate the area under the epithelium from about 2 weeks p.p. A few IgM, IgG- and IgA-bearing B cells are already present at 4 days, and rapidly increase in numbers; T cells usually appear at day 8. Discrete T- and B-cell areas do not appear until 4 weeks and are only observed regularly after 12 weeks, when secondary follicles appear. BALT starts development at a similar time to other peripheral lymphoid organs but apparently achieves immunological activity later. It is concluded that antigens probably play an important part in organising BALT.