Immunohistologic detection of the primary follicle (PF) in human fetal and newborn lymph node anlages

Age-related changes of the human splenic marginal zone B cell compartment

In this review, we will summarize the growing body of knowledge on the age-related changes of human splenic B cell composition and molecular evidence of immune maturation and discuss the contribution of these changes on splenic protective function. From birth on, the splenic marginal zone (sMZ) contains a specialized B cell subpopulation, which recruits and archives memory B cells from immune responses throughout the organism. The quality of sMZ B cell responses is augmented by germinal center (GC)-dependent maturation of memory B cells during childhood, however, in old age, these mechanisms likely contribute to waning of splenic protective function.

Development of human lymph nodes and Peyer's patches

In contrast to our understanding of murine lymphoid organogenesis, detailed knowledge on the mechanisms of human lymph node development is virtually lacking. This is mainly due to the obvious difficulties that accompany research using human fetal organs. In this review we will highlight current knowledge on human lymph node and Peyer's patch development and will temporally align observations made in humans with data available from murine studies. In the final paragraphs we will put this knowledge in the context of human malignancies in which interactions between lymphocytes and stroma, resembling those seen in lymphoid organs, are recapitulated.

The postnatal maturation of the immunoglobulin heavy chain IgG repertoire in human preterm neonates is slower than in term neonates

During the perinatal period the development of the IgH chain CDR3 (CDR-H3) repertoire of IgM transcripts is maturity-dependent and not influenced by premature exposure to Ag. To study whether maturity-dependent restrictions also predominate in the perinatal IgG repertoire we compared 1000 IgG transcripts from cord blood and venous blood of extremely preterm neonates (24-28 wk of gestation) and of term neonates from birth until early infancy with those of adults. We found the following. First, premature contact with the extrauterine environment induced the premature development of an IgG repertoire. However after preterm birth the diversification of the IgG repertoire was slower than that after term birth. Second, the IgG repertoire of preterm neonates retained immature characteristics such as short CDR-H3 regions and overrepresentation of D(H)7-27. Third, despite premature exposure to the extrauterine environment, somatic mutation frequency in IgG transcripts of preterm infants remained low until they reached a postconceptional age corresponding to the end of term gestation. Thereafter, somatic mutations accumulated with age at similar rates in preterm and term neonates and reached 30% of the adult level after 6 mo. In conclusion, class switch was inducible already at the beginning of the third trimester of gestation, but the developing IgG repertoire was characterized by similar restrictions as those of the developing IgM repertoire. Those B cells expressing more "mature" H chain sequences were not preferentially selected into the IgG repertoire. Therefore, the postnatal IgG repertoire of preterm infants until the expected date of delivery differs from the postnatal repertoire of term neonates.

Resistance of neonatal mice to scrapie is associated with inefficient infection of the immature spleen

Previous studies demonstrated that neonatal mice up to about a week old are less susceptible than adult mice to infection by intraperitoneal inoculation with mouse-passaged scrapie. In peripherally inoculated adult mice, scrapie replicates in lymphoid tissues such as the spleen before invading the central nervous system. Here, we investigated scrapie susceptibility in neonatal mice in more detail, concentrating on spleen involvement. First, we demonstrated that neonatal mice are about 10 times less susceptible than adults to intraperitoneal scrapie inoculation. Then we injected mice intraperitoneally with a scrapie dose that produced disease in all mice inoculated at 10 days or older but in only about a third of neonatally inoculated mice. In this experiment, spleens collected 70 days after scrapie injection of mice 10 days old or older almost all contained pathological prion protein, PrPSc, and those that were bioassayed all contained high infectivity levels. In contrast, at this early stage, only two of six spleens from neonatally inoculated mice had detectable, low infectivity levels; no PrPSc was detected, even in the two spleens. Therefore, neonatal mice have an impaired ability to replicate scrapie in their spleens, suggesting that replication sites are absent or sparse at birth but mature within 10 days. The increase in susceptibility with age correlated with the first immunocytochemical detection of the normal cellular form of prion protein, PrPc, on maturing follicular dendritic cell networks. As lymphoid tissues are more mature at birth in sheep, cattle, and humans than in mice, our results suggest that in utero infection with scrapie-like agents is theoretically possible in these species.

Development, maturation and subsequent activation of follicular dendritic cells (FDC): immunohistochemical observation of human fetal and adult lymph nodes

To elucidate the processes involved in development and activation of human follicular dendritic cells (FDC), immunohistochemistry was performed on paraffin sections of fetal lymph nodes (FLN) obtained from archived autopsy material, and of adult reactive lymph nodes (ARLNs) excised for diagnostic purpose, using a panel of antibodies. Our study showed that tiny clusters of CNA.42(+ )KiM4p(+) cells, surrounded by some B-lymphocytes, initially arose in the cortical area of underdeveloped FLN around the 20th gestational week. No co-expression of CD21 and CD35 was found. In the relatively developed FLN of the same gestational age, small eddies of immature FDC, which expressed CD21, CD35, and nerve growth factor receptor (NGFR), as well as CNA.42 and KiM4p, were observed within ill-defined aggregations of B-lymphocytes. As gestation progressed, more B-lymphocytes assembled in a compact manner and formed primary lymphoid follicles containing an extending web of mature FDC, which expressed CNA.42, KiM4p, CD21, CD35, NGFR, and sometimes CD23 and X-11. In well-developed secondary follicles of ARLNs, activated FDC expressed additional molecules such as CD55, CD106, and S100alpha. Our observations identified the processes of phenotypic alteration of human FDC and established practical indicators determining their developmental stage and functional phase.

Evolution of classic Hodgkin lymphoma in correlation to changes in the lymphoid organ structure of vertebrates

In order to integrate evolutionary concepts into lymphoma research we mapped features of classic Hodgkin lymphoma (a disease which has been recently described to be derived from germinal center B-cells) onto a phylogenetic tree of vertebrates. Secondly, we matched the phylogenetic occurrence of classic Hodgkin lymphoma to the changes in the lymphoid organ structure during vertebrate evolution. According to our analysis, classic Hodgkin lymphoma evolved exclusively at the developmental stage of mammals. Interestingly the appearance of Hodgkin lymphoma is correlated to the evolution of germinal centers in mammals. This lends some credit to the hypothesis that genes specific to the germinal center reaction are involved in the pathogenesis of Hodgkin lymphoma. However, as evolution did not stop at the developmental stage of the mammalian stem-species, to a certain extent species with specific differences of classic Hodgkin lymphoma can be expected. One such difference is that classic Hodgkin lymphoma occurs with a significantly higher frequency in humans than in all other mammals. This could be partially due to Epstein-Barr virus (EBV) infection in approximately 40%-50% of Hodgkin disease cases, that is associated with an expression of the EBV-encoded oncogen LMP-1. In conclusion we propose that the mapping of lymphoma related characteristics onto a phylogenetic tree is a valuable new tool in lymphoma research.

Diversification of Ig heavy chain genes in human preterm neonates prematurely exposed to environmental antigens

Preterm neonates are exposed to extrauterine environmental Ags during the time period that corresponds to the last trimester of normal intrauterine development. To study whether this precocious exposure to Ags accelerates the Ig repertoire diversification, we compared IgH chain genes of preterm neonates (gestational age, 25-29 wk) during their first postnatal months with those of term neonates. Preterm infants approaching their expected date of delivery after 8-13 wk of extrauterine life used a similar V(H), D(H), and J(H) gene segment repertoire as term neonates born after intrauterine development. Furthermore, the length increase of the NDN region between V(H) and J(H) by 0.25 nt per gestational week (r = 0.556, p < 0.0001) was not accelerated. Thus, the generation of the V(H) region gene repertoire is developmentally controlled and independent of environmental influences. However, exposure to extrauterine Ags induced class switch and somatic mutations in IgH chain genes within 2 wk after premature birth and IgG transcript diversity and mutational frequency increased with the duration of extrauterine life. Three-month-old preterm infants expressed a heterogeneous IgG repertoire at their expected date of delivery with V(H) region genes carrying significant numbers of somatic mutations with evidence for Ag selection. Term neonates, however, had no such IgG repertoire. We conclude that restrictions in the neonatal Ig V(H) region gene repertoire persist until term despite exposure to environmental Ags. Yet, many weeks before term the immune system of the preterm neonate can already support germinal center reactions in response to environmental Ags.

Transplantation and growth characteristics of human fetal lymph node in immunodeficient mice

OBJECTIVE

The lymph node is an integral component of the immune system and the major site of antigen-dependent lymphocyte proliferation and differentiation. Development of animal models possessing functional primary human lymph nodes will have a significant impact on research in lymphopoiesis and immune response. To date, successful transplantation of primary human lymph nodes in rodents has not yet been reported. This work was undertaken to develop a reliable methodology to engraft primary human fetal lymph nodes in immunodeficient mice.

MATERIALS AND METHODS

Three different sets of parameters, including three different transplantation sites in the mice, two different strains of immunodeficient mice, and two different preconditioning regimens, were evaluated. The growth characteristics of the implanted primary human fetal lymph nodes were examined 3 months after transplantation by histologic, immunocytochemical, and flow cytometric methods.

RESULTS

Transplantation of primary human fetal lymph nodes into subcutaneous pouches in the ears in severe combined immunodeficiency (SCID) mice preconditioned with etoposide reproducibly give rise to >80% engraftment. The engrafted primary human fetal lymph nodes undergo massive growth (>200-fold) and retain the same histology and cellular composition as fresh human fetal lymph nodes from the same donors.

CONCLUSIONS

We report, for the first time, the development of a reliable methodology to successfully engraft human fetal lymph node in SCID mice. The engrafted human lymph nodes are visible and accessible to experimental manipulations. This SCID-hu mouse model with human lymph node should provide a physiologically relevant system to investigate lymphopoiesis, immunologic response, and virus-mediated immunosuppression.

Blastic variant of mantle cell lymphoma shows a heterogenous pattern of somatic mutations of the rearranged immunoglobulin heavy chain variable genes

Mantle cell lymphoma is a distinct clinicopathological entity associated with t(11;14) and cyclin D1 overexpression. The majority of cases show uniform morphological and phenotypic features characterized by a monotonous proliferation of small-to-medium-sized irregular B cells that express CD5 and bright surface immunoglobulin IgM and IgD. By sequence analysis of the rearranged immunoglobulin heavy chain variable genes (VH), it has been shown that these lymphoma cells carry little if no somatic mutations, as described for the fetal CD5+ cells or B1 cells. Besides mantle cell lymphoma with classic histological features, a morphological variant of mantle cell lymphoma with blastic features and a more aggressive clinical course has been described. To investigate whether this variant is closely related, by the cell of origin, to typical cases, we analysed the presence and the pattern of somatic mutations of the VH genes in a series of nine cases diagnosed as such. Our cases of blastic mantle cell lymphomas rearrange most frequently VH4 and VH3 family genes. In three cases there was a complete homology to published germline genes, and a near complete homology was documented in another three. In contrast, the remaining three cases showed somatic mutations in their rearranged VH genes. Mutation analysis revealed evidence for antigen selection in one of these three cases. Taken together, these data are similar to those of normal adult-type B1 cells and those described for chronic lymphocytic leukaemia (CLL) but slightly different to those reported for classic mantle cell lymphoma. It is likely that blastic mantle cell lymphoma as well as CLL originates from adult-type B1 cells. More cases will need to be studied to determine whether classic mantle cell lymphoma is different from the blastic subtype and if it arises from fetal-type B1 cells.

Immunohistochemistry of 'tertiary lymphoid follicles' in oral amalgam-associated lichenoid lesions

OBJECTIVES

To characterise lymphoid follicle-like aggregates incidentally found to occur in biopsies of oral lichenoid reactions (OLR) and to correlate the findings to hyperplastic tonsil follicles.

DESIGN

An immunocytochemical analysis of archival material.

SUBJECTS AND METHODS

In an arbitrarily selected period 1992-1994 with a total of 13,924 oral biopsies, 2407 cases were signed out as OLR or lichen planus. These were microscopically reviewed, with the purpose to retrieve all cases showing histologic changes resembling secondary lymphoid follicles.

RESULTS

87 cases showed lymphoid follicle-like changes and 82 of these were in oral regions known to constitutively lack 'organised MALT'. Unexpectedly, all of the 82 were found retrospectively to be in close or direct contact with amalgam fillings. Immunocytochemically, using antibodies to B and T cells, macrophages, follicular dendritic cells and proliferation and apoptosis markers, the mucosal follicles stained similar to tonsillar secondary follicles. In several of an additional 11 OLR cases with histologic changes suggestive of primary follicles, we also found immunocytochemical evidence of such changes.

CONCLUSIONS

'Tertiary lymphoid follicles' may occasionally develop in OLR at sites of the oral mucosa constitutively lacking organised lymphoid tissue. The microenvironment of the OLR T cell infiltrate may occasionally favour such follicle development and amalgam constituents may causally be involved in an unknown way.