Aging of the lymphoid system at the organ level. With special reference to the bone marrow as site of antibody production

Age-related changes in lymphocyte development and function

The effects of aging on the immune system are widespread and extend from hematopoietic stem cells and lymphoid progenitors in the bone marrow and thymus to mature lymphocytes in secondary lymphoid organs. These changes combine to result in a diminution of immune responsiveness in the elderly. This review aims to provide an overview of age-related changes in lymphocyte development and function and discusses current controversies in the field of aging research.

Repertoire of antibody response in bone marrow and the memory response are differentially affected in aging mice

The primary burst of Ab and germinal center (GC) formation in response to T-dependent Ag is compromised in aging mice. Here we examine the effects of aging on the post-GC phase of memory B cell differentiation and the late Ab repertoire maturation in bone marrow (BM) in mice immunized with a hapten nitrophenyl coupled to chicken gamma-globulin. Specific Ab-forming cells (AFC) with mutated V(H) genes accumulated preferentially in the BM of aged mice, although the AFC numbers and average number of mutations per V(H) were lower, and the D gene usage was less restricted compared with those in the young animals. However, the repertoire of AFC after an Ag boost demonstrated the hallmarks of Ag selection, including the recurrent mutations and canonical VD rearrangements, similar to the late primary response in young animals. It is postulated that the Ab repertoire maturation in aged mice is delayed and may be notably improved by repeated immunizations.

Canonical germinal center B cells may not dominate the memory response to antigenic challenge

Spleen and bone marrow (BM) are the major sites of antibody production and anamnestic response in systemically immunized mice. We examined the VDJ segment repertoire of antibody plaque-forming cells (APFC) in those two sites in the course of antibody responses to the hapten nitrophenyl (NP). Individual IgG APFC expressed any one of 10 V(H) segments of the V186.2/V3 (J558) gene family: 186.2, 102, 23, C1H4, 165.l, CH10, 3, 593.3, 24.8 and 671.5. The majority of cells in both spleen and BM expressed the V186.2 gene joined to a D segment with Tyr95. During a 2-month period after a single immunization, the V186.2(+) APFC in BM accumulated 3 times as many somatic mutations than splenic APFC (average 8.5 versus 3 mutations/V(H)); this process was T(h) dependent as shown by in vivo depletion of CD4(+) lymphocytes. However, the V186.2(+) APFC in both spleen and BM shared a recurrent W33L replacement, indicating their common origin from germinal centers. The APFC expressing the other (analogue) V(H) segments were evenly represented in the spleen and BM, but they accumulated few, if any, mutations. The anamnestic V186.2(+) APFC were highly mutated both in the spleen and BM; they represented a new and unexpected clonotype. The V/D segments were joined by Gly95 instead of Tyr95, the W33L was absent and a new shared K58R replacement appeared. The APFC expressing the 'analogue' V(H) genes comprised approximately 20% of the anamnestic response and did not accumulate more mutations, but their affinities were in the range of the memory V186.2(+) cells. These data suggest that the late primary and secondary responses to a hapten may be born by different B cell lineages, and that some clonotypes may reach the memory pool without an extensive mutation and expansion.

Bone marrow response to acute and chronic Trypanosoma congolense infection in multimammate rats (Mastomys coucha)

The femoral bone marrow of multimammate rats (n=90), aged 3-8 weeks, experimentally infected with different doses of Trypanosoma congolense was examined by light and electron microscopy. Some animals died from trypanosomosis, but groups of 10 were killed at 4-8, 9-16, 20-24, 30, 40, 50 and 60 days post-infection (dpi). In the acute stage of infection (4-8 dpi) the bone marrow invariably showed a striking increase in erythropoiesis, characterized by an increase in the number of mitotic figures and erythroblastic islands and by a marked decrease in the myeloid:erythroid cell ratio. Later in the infection, erythropoietic activity decreased, while erythrophagocytosis, granulopoiesis, megakaryopoiesis and plasma cell population increased. In chronic infection (16-60 dpi), erythropoietic activity decreased, while intra- and extra-vascular erythrophagocytosis greatly increased. There was also an increase in the bone marrow stroma cells. Excessive erythrophagocytosis by these cells led to the formation of myelin figures and cytoplasmic telephagolysosomes. Degeneration and necrosis of neutrophils lining the adluminal surfaces of the blood sinuses were observed. It is concluded that in the acute stage of the infection, the bone marrow is responsive to the anaemia and that in the chronic stage, dyserythropoiesis and increased erythrophagocytosis by the expanded and activated cells of the mononuclear phagocytic system play an important role in the production of anaemia.

Development of the natural response of immunoglobulin secreting cells in the pig as a function of organ, age and housing

We analysed the development of the natural immunoglobulin-secreting cell (Ig-SC) response in systemic- and mucosal-lymphoid tissues of specified pathogen free pigs between 1 and 40 weeks of age. As antigen exposure may influence the development of the Ig-SC repertoire we also compared the frequencies of Ig-SC in various lymphoid tissues of 40 weeks old specified pathogen free pigs and conventional pigs. A procedure to isolate lamina propria cells from porcine intestine was adapted for this study. The frequencies of IgM-, IgG-, and IgA-secreting (spot forming) cells were determined with a reversed enzyme linked immunospot assay, which was also adapted for detection of Ig-SC in pigs. The Ig-SC frequencies were calculated as percentage of the mononuclear leukocytes isolated from the various organs. The observations till 40 weeks of age were as follows: Splenic IgM-SC predominated at all ages and reached a plateau of 0.1-0.2% of the mononuclear leukocytes already at 4 weeks of age. The IgM-SC of mesenteric lymph node (MLN) predominated up till 12 weeks of age and reached an optimum of 0.15% reached at 4 weeks of age. The frequencies of IgG-SC of spleen and MLN had dips around 4 weeks of age and increased thereafter till 40 weeks of age (spleen 0.025%, MLN 0.05% at 40 weeks of age). The frequencies of IgA-SC were low in the spleen (< or =0.003%) and moderate in the MLN (0.01-0.02%) at all ages tested. In peripheral lymph node (PLN) and bone marrow (BM), the frequencies of IgM-SC (0.03-0.05%) were much lower than in the spleen. The IgG-SC frequencies of BM and MLN also had dips around 4 weeks of age and increased thereafter. The IgG-SC frequency of BM reached a plateau at 12 weeks of age (0.15%) and for PLN the highest frequency was observed at 40 weeks of age (0.05%). The frequencies of IgA-SC were low in BM and PLN (<0.003%). High frequencies of IgA-SC were observed in mucosa associated tissue like Peyer's patches (PP) and intestinal lamina propria (till 20% of the mononuclear leukocytes in intestinal lamina propria of 12-40 weeks of age). IgM and IgA are both important isotypes in mucosal lymphoid organs in the pig. The shift from IgM to IgAas predominant, mucosal isotype was first observed in duodenum and jejunum (12 weeks) and later in ileum (40 weeks). The influence of ageing on the frequency of Ig-SC in PP was only observed in jejunal PP. whereas in ileal PP the frequencies of Ig-SC did not vary over time. We combined our data about the frequencies of IgM-, IgG-, and IgA-SC in various organs with data obtained by others about the distribution of lymphocytes over porcine lymphoid organs at about 12 weeks of age. Based on these calculations we concluded that the small intestine, with more than 80% of all Ig-SC, is fair most the major site of Ig production in the pig. We also concluded that the small intestine is the major site of IgA and IgM production cells in the pig. Although IgA becomes predominant along the intestine, the results demonstrated that in the pig IgM is more a mucosal isotype compared with other species. With 40% of all IgG-SC the porcine BM appeared to be the major site of IgG production. Unexpected results were obtained for IgG-SC in the systemic lymphoid organs. In these organs the frequencies of IgG-SC dropped firstly from 1 to 4 weeks of age and steadily increased thereafter till 40 weeks of age. This observation is discussed in relation to the possibility that systemic IgG-SC at one week of age were passively acquired from maternal colostrum. The influence of housing/antigenic load at 40 weeks of age was mainly expressed by an increase (2-8x) of the frequency of IgG-SC in spleen, PLN, BM, and intestinal lamina propria, whereas the typical mucosal IgA-SC frequencies in the lamina propria were hardly affected.

Characterization of CD4+ T cells in mouse bone marrow. I. Increased activated/memory phenotype and altered TCR Vbeta repertoire

A significant proportion of memory B cells home to bone marrow (BM) which is a major site of anamnestic antibody responses in mice. We hypothesized that memory T cells likewise accumulate in BM perhaps to provide help for antibody production, and that the compartment of CD4+ T cells in BM of unimmunized mice would be enriched for memory phenotype cells that might have been activated by environmental antigens. The phenotype of activated/memory CD4+ lymphocytes has been defined as CD44hi CD45RBlo CD62L-. Conversely, the phenotype of immunologically naive cells is CD44lo CD45RBhi CD62L+. Flow cytrometric analysis of tissue from normal, adult C57BL/6 mice identified 1-2 % CD3+CD4+ cells in BM. Up to 40 % of CD3+CD4+ cells in the BM expressed the activated/memory phenotype compared with < or = 10% in the spleen and lymph nodes. Analysis of TCR Vbeta repertoire revealed that expression of Vbeta3 and Vbeta7 genes was increased as much as fourfold in BM compared to the periphery; most of this increase was within the CD44hi T cells. The accumulation of activated/memory T cells and clonotypic expansion(s) was not seen in the BM of germ-free mice, indicating that it reflects the history of the animal's exposure to antigens. Finally, immunization of mice which express a transgenic T cell receptor specific for ovalbumin peptide resulted in appearance of antigen-specific T cells with activated/memory phenotype in the BM.

Long-term antibodies after an oral immunization with cholera toxin are synthesized in the bone marrow and may play a role in the regulation of memory B-cell maintenance at systemic and mucosal sites

To study the importance of the bone marrow in the long-term antibody response, IgG and IgA antitoxin antibody-forming cells were evaluated by ELISPOT in Peyer's patches, mesenteric lymph nodes, spleen, lamina propria of the small intestine and bone marrow at several times after oral immunization with cholera toxin. The mesenteric lymph node was the site having the major frequency of IgG antitoxin during the first two weeks after priming, whereas lamina propria was the site with a major number of IgA antitoxin antibody-forming cells. However, from 3 weeks until 10 months after priming, bone marrow became the site with the major frequency of IgG, and especially IgA antitoxin antibody-forming cells (without taking into account the lamina propria). This result indicates that bone marrow was responsible for the long-term antibody response and raises questions concerning the mechanisms involved in the maintenance of antibody production. The importance of bone marrow as a site of antibody production was great when we analysed results as the true contribution of the total number of antitoxin antibody-forming cells, taking into account the number of cells recovered from each organ. When we analysed the anatomical location of memory B and T cells by adoptive transference, we found that cells from mesenteric lymph nodes and spleen were able to transfer a strong antibody response to naive syngeneic recipients, whereas bone marrow cells transferred a weak antibody response.

Regulation of autoimmunity in normal and rheumatoid individuals by bone marrow-derived natural suppressor cells and their suppressor factor: BDSF

Natural suppressor activity is defined as the ability of unstimulated effector cells to suppress responses of lymphoid cells to antigenic and mitogenic stimuli in an MHC unrestricted manner. We have described natural suppressor cells in bone marrow exerting such a function through a suppressor factor termed BDSF. In this report we demonstrate the ability of BDSF to regulate the in vitro EBV- and PWM-induced production of both IgM and IgM rheumatoid factor antibodies of lymphoid cells obtained from normal individuals and those with rheumatoid arthritis. BDSF therefore may play a role in the normal BM microenvironment suppressing primary IgM antibody responses. Since autoantibody responses are similarly suppressed, functional alteration or lack of BDSF may be responsible for the emergence of autoantibody-producing cells in bone marrow during certain autoimmune states.

Human bone marrow-derived IgA is produced by IgA-committed B cells in vitro

Although human bone marrow has been implicated in the production of serum immunoglobulins, little information is available concerning the kinetics of antibody production (primary- or secondary-type humoral response) or the cells that are responsible for antibody production in human bone marrow. In this study, the kinetics of and cells responsible for antibody production in the bone marrow were investigated. Previous studies have demonstrated that human bone marrow mononuclear cells secrete a significant amount of IgA in vitro. This finding led to the focus of the present investigation on bone marrow IgA production. The results reported here demonstrate that IgA was synthesized de novo in cultures of bone marrow mononuclear cells; its peak concentration in the culture supernatants preceded that of IgM; its production was totally inhibited by the addition of microgram quantities of anti-alpha-chain antiserum, while milligram quantities of anti-mu-chain antiserum were required for even partial inhibition of IgA production; and the culture of isolated IgA-bearing cells resulted in a greater than 13-fold increase in IgA concentration in the culture supernatants as compared with those from unseparated bone marrow mononuclear cells. From this study, it was concluded that bone marrow produces IgA as a secondary or anamnestic response to some undetermined stimulus and that IgA-committed B cells residing in, although probably not stimulated in, the bone marrow compartment were responsible for the IgA synthesis and secretion in vitro.

Cells involved in the immune response. XXXI. The role of the spleen in the primary and secondary immune responses in the normal adult outbred rabbit: the initial localization of memory cells to the spleen and their subsequent dissemination to the thymus and peripheral lymph nodes

Normal adult outbred rabbits were immunized intravenously (iv) with sheep erythrocytes (SRBC). At varying times thereafter, the different lymphoid organs were investigated for spontaneous and culture-induced antibody secreting cells by the aqueous hemolytic plaque-forming cell (PFC) technique. During the phase of active antibody formation (Days 3 to 30), immediate PFC, indicative of spontaneous antibody synthesis and secretion, were detected principally in the spleen. In the early postimmune memory period (Days 30 to 90), memory cells capable of generating PFC following secondary immunization in in vitro culture with SRBC were detected only in the spleen. However, by 4 months postimmunization, memory cells were detected in the thymus and popliteal lymph node (PLN) as well as in the spleen. The number of memory cells in the thymus and PLN was significantly higher by 6 months postprimary iv immunization and was even further elevated by 9 months postprimary iv immunization. Following in vivo secondary immunization by the iv injection of SRBC 2 or 6 months postprimary immunization, immediate PFC were detected in large numbers in the spleen, the bone marrow, and the blood, marginally in the PLN and not at all in the thymus. Similar results were obtained at 9 months following primary immunization with SRBC with the exception that large numbers of immediate PFC were detected in the PLN following secondary iv immunization. Following culture of these lymphoid cells for 5 days in vitro with SRBC, the thymus and PLN cells, as well as the spleen cells, generated large numbers of PFC. Since immediate PFC were never detected among the freshly isolated thymus cells whereas thymic cell cultures 6 and 9 months postprimary iv immunization invariably generated large numbers of PFC following secondary immunization in vitro, the thymus memory cells would appear to be inaccessible to particulate antigen injected intravenously; they can only be detected following activation by the antigen in culture. The PFC generated by thymus memory cells (and spleen and PLN) were totally inhibited by the inclusion of sheep anti-rabbit IgG into the PFC assay. This finding demonstrates unequivocally that the plaques induced by thymus cells, just as the plaques induced by spleen and PLN cells, are antibody mediated and not false plaques. Therefore, the thymic PFC cells must be antibody-secreting B-memory cells since T cells do not synthesize or secrete immunoglobulins.

Graft-vs.-host reactions: mechanisms and contemporary theories

A graft-vs.-host (GvH) reaction can be initiated by injection of immunocompetent lymphocytes into a histoincompatible host that is unable to reject these cells. The reaction is characterized by splenomegaly, hepatomegaly, lymph node atrophy, body weight loss, dermatitis, and diarrhea, often leading to mortality. The onset and severity of the GvH reaction are determined by differences in histocompatibility antigens between the donor and the acceptor, and by the number and nature of the transplanted allogeneic cells. Many different in vivo and in vitro systems have been devised for experimental studies of the GvH reaction. In several of these models, however, different parameters are measured. Furthermore, the conclusions drawn from these investigations sometimes contradict each other. This paper reviews the experimental data, and discusses the mechanisms underlying the GvH reaction.

Age-related change of distribution of immunoglobulin containing cells in human bone marrow. Changes in patients with benign monoclonal gammopathy and multiple myeloma

The number and mode of distribution of immunoglobulin containing cells in human bone marrow were investigated immunohistochemically using paraffin sections of bone marrow aspirates. In individuals without specific diseases, the number of immunoglobulin containing cells per unit field in bone marrow increased with advancing age until the 3rd decade and leveled off thereafter. The magnitude of the increase was great for Ig-G and Ig-A, but very slight for Ig-M. Such age-related change in the number of Ig-G and Ig-M containing cells in bone marrow was almost comparable to the age-related change of serum level of Ig-G and Ig-M. However, the magnitude of age-related increase of Ig-A containing cells in bone marrow was apparently higher than that of the serum level of Ig-A. Cluster formation of immunoglobulin containing cells increased with age in terms of both incidence and size. Three points were suggested for differentiation of benign monoclonal gammopathy (BMG) from multiple myeloma (MM). First, the ratio of serum level of M-component divided by the average number of immunoglobulin containing cells per unit field was higher in BMG than in MM; second, the number of cells per cluster of immunoglobulin containing cells was more than 50 in MM, but that in BMG less than 20; third, the small immunoglobulin containing cells with narrow cytoplasm were more prominent in MM than in BMG.

Histology of the bone marrow antibody response. An immunocytochemical study during the secondary response in mouse and rat

The histology of the specific and non-specific antibody response in mouse and rat bone marrow was studied after subcutaneous priming and intravenous boosting with horseradish peroxidase (HRP). Cells producing specific antibody against HRP were found only occasionally in the bone marrow after subcutaneous priming. After the intravenous boost injection their number gradually increased. These anti-HRP forming cells were found as single cells, randomly dispersed throughout the bone marrow. Such a random distribution was also found for cytoplasmic (non-specific) immunoglobulin containing cells. At no time point after immunization could lymphoid aggregates or trapping of immune complexes be observed in the bone marrow of either species. On the basis of these observations it is concluded that the bone marrow forms a suitable microenvironment for immigrating antibody-forming cells but does not contribute actively to the induction of the immune response.