Double immunocytochemical evidence for a clonal development of specific antibody-containing cells in the rabbit spleen

Is there a single differentiation pathway for all antibody-forming cells in the spleen?

By incubating tissue sections with antigen (or hapten)-enzyme conjugates, followed by enzyme cytochemistry(1-4), N. van Rooijen and his colleagues have been able to study the development and localization of specific antibody-producing cells in the spleen of animals after a single intravenous antigen injection. Variations in this method(5-11) allowed them to compare the localization patterns of cells producing different antibodies and to determine simultaneously their Ig isotype. Studies on primary and secondary immune responses against thymus-dependent and thymus-independent antigens lead them to postulate that there is one 'differentiation pathway' for antibody-forming cells in the spleen, independent of the antigen and the type of immune response.

Gene Conversion and Hypermutation During Diversification of VH Sequences in Developing Splenic Germinal Centers of Immunized Rabbits

The young rabbit appendix and the chicken bursa of Fabricius are primary lymphoid organs where the B cell Ab repertoire develops in germinal centers (GCs) mainly by a gene conversion-like process. In human and mouse, V-gene diversification by somatic hypermutation in GCs of secondary lymphoid organs leads to affinity maturation. We asked whether gene conversion, somatic hypermutation, or both occur in rabbit splenic GCs during responses to the hapten DNP. We determined DNA sequences of rearranged heavy and light chain V region gene segments in single cells from developing DNP-specific GCs after immunization with DNP-bovine γ-globulin and conclude that the changes at the DNA level that may lead to affinity maturation occur by both gene conversion and hypermutation. Selection was suggested by finding some recurrent amino acid replacements that may contribute increased affinity for antigen in the complementarity-determining region sequences of independently evolved clones, and a narrower range of complementarity-determining region 3 lengths at day 15. Some of the alterations of sequence may also lead to new members of the B cell repertoire in adult rabbits comparable with those produced in gut associated lymphoid tissues of young rabbits.

Localization in the rat spleen of carbon-laden macrophages introduced into the splenic artery: a subpopulation of macrophages entering the white pulp

Heavily carbon-laden (HC) macrophages, largely derived from the red pulp of the donor spleen, were injected into the splenic artery of recipient rats. Immediately after injection, HC macrophages were found only in the marginal sinus and in the splenic cords. With time after injection, they appeared successively at the periphery of the white pulp, in the deeper white pulp, and finally in and near the germinal centers, suggesting migration of HC macrophages from the marginal sinus towards the germinal centers. The number of HC macrophages in and near the germinal centers reached a peak at 12 h. Most of the HC macrophages in the white pulp were spherical or ovoid in shape with a diameter of 7-11 microns in sections, having an eccentric round or oval nucleus often with a distinct nucleolus and a cap-like or horseshoe-like cytoplasm filled with carbon. When immunostained with monoclonal antibodies against rat macrophage subpopulations, more than 90% of HC macrophages in the white pulp were found to be ED1+2-3-. A population of the same type of macrophages, both in morphology and phenotype, were found in the red pulp of the donor spleen. They were different from the major residents, red pulp scavenger macrophages, which were ED1+2+3- and larger in size and irregular in shape. These results suggest the presence of a distinct subpopulation of macrophages which actively migrate into the splenic white pulp including the germinal centers. A discharge of transferred macrophages from the red pulp to the general circulation is also suggested.

Kinetics of germinal center development in lymph nodes of young and aging immune mice

Recent findings imply that germinal center paucity in old mice, at least in part, results from a defect in the mechanisms responsible for the transport of antigens to lymphoid nodules (follicles) and the consequent impairment of the antigen retaining reticulum (ARR) of follicular dendritic cells (FDCs). The present objective was to observe the kinetics of lymph node germinal center development in old mice having antigen transport and ARR deficits. Germinal center development was monitored in popliteal (PLN) and axillary (AXLN) lymph nodes of 6-8 wk and 23-mo-old horseradish peroxidase (HRP) immune C57BL/6 mice. Using the selective binding of germinal center B cells for peanut agglutinin (PNA), germinal centers were identified in serial vibratome sections following histochemical labeling with PNA-peroxidase conjugates at times 0, 15 min, 1, 3, 5, and 10 days after footpad challenge with 8 micrograms HRP. To follow the fate of preexisting (environmental antigen-induced) germinal centers and the development of de novo (HRP-induced) germinal centers, it was essential to distinguish between these germinal centers. Accordingly, PNA positive germinal centers associated with HRP-retaining (peroxidase positive) ARR were identified as de novo germinal centers and germinal centers not associated with a peroxidase positive ARR were classified as preexisting germinal centers. Kinetic analysis of PNA positive germinal centers showed the following: 1) Preexisting, environmentally-induced germinal centers dissociated and disappeared by day 3 as indicated by a decline in their numbers after antigen injection: the process of germinal center dissociation remained unaffected by aging. 2) The latency of de novo germinal center appearance was approximately equal in duration (approximately 3 days) to the disappearance of pre-existing germinal centers. 3) The number and size of de novo HRP-induced germinal centers increased through the experimental period in young lymph nodes, but in old mice these parameters were depressed, resulting in a significant germinal center deficit. 4) The ratio of HRP-retaining ARR to de novo induced germinal centers was 1:1 in young and responder old mice. This ratio was not affected by aging. This finding favored the concept that antigen retention in ARR is a requirement of germinal center development. The observations supported our hypothesis that germinal center development, at least in part, depends on a normal antigen transport by showing that in aged mice with defective antigen transport-related ARR and iccosome deficits there is an impaired development of germinal centers.

The "in situ" immune response in lymph nodes: a review

For many years data on the development of specific antibody-forming cells in lymph nodes were incomplete, fragmentary, and even contradictory. A number of recent studies have been performed, concerning 1) their overall architecture; 2) migration of B-lymphocytes; 3) localization of accessory cells and T-lymphocytes which are believed to be involved in humoral immune responses; and 4) localization patterns of specific antibody-forming cells developing during thymus dependent and thymus independent immune responses. Comparison of these new results with those of earlier studies suggests a single route of migration followed by all cells which will differentiate into antibody-forming cells. During their differentiation into antibody-forming plasma cells, antigen reactive B-cells migrate along the required accessory cells and/or T-lymphocytes.

Development of specific antibody-forming cells in various lymphoid organs of rabbit after intravenous antigen administration

Rabbits were intravenously primed and boosted with trinitrophenyl-keyhole limpet hemocyanin (TNP-KLH) and human serum albumin (HSA); both antigens were injected simultaneously. The localization of anti-TNP-antibody-forming cells (AFCs) and anti-HSA-AFCs was determined in various lymphoid organs of the rabbit. In all lymphoid organs of primed rabbits anti-TNP-AFCs outnumbered anti-HSA-AFCs, with the exception of the thymus, in which neither of them was encountered. In the spleen the antibody-forming cells were mainly situated in the periphery of the periarteriolar lymphocyte sheaths (PALS) and in the coaxial sheaths of lymphoid tissue surrounding the terminal arterioles. In the lymphoepithelial organs AFCs were almost exclusively situated in the interfollicular areas, and in the lymph nodes largely in the medulla. An intravenous booster injection led to a secondary immune response (i.e., increase of AFCs) in the spleen. No visible change in the number of specific AFCs was observed in the lymphoepithelial organs. However, in the mesenteric and popliteal lymph node the number of anti-TNP-AFCs had increased tremendously.

The early postnatal development of the primary immune response in TNP-KLH-stimulated popliteal lymph node in the rat

The popliteal lymph nodes were removed from young rats of various ages five days after a single immunization with TNP-KLH in the hind footpads. Cryostat sections of the lymph nodes were investigated by means of enzyme- and immunohistochemical techniques at the light-microscopical level. The presence and localization of anti-TNP antibody-containing cells were examined using a new technique to visualize specific antibodies. Moreover, the development of the lymph nodes following exogenous antigenic stimulation was compared with that of unstimulated lymph nodes. Specific antibody-containing cells could not be found before day 15 after birth, in rats immunized at day 10. From that time these lymphoid cells were located primarily at the border between cortex and medulla. Younger popliteal lymph nodes showed only aspecific immunoglobulin-containing lymphoid cells. With age, the number of specific antibody-containing cells tended to increase. These cells were more mature, according to morphological criteria and were located nearer the medulla. The first primary follicles were seen at day 19, as was the case in unstimulated animals. The first secondary follicles, containing germinal centers, were detected at day 23, whereas in unstimulated popliteal lymph nodes they were never found. Trapping of immune complexes could not be demonstrated before day 33 after birth. The later appearance of this phenomenon might be a consequence of the techniques applied to demonstrate specific antibody-containing cells.

Recent advances in the detection and characterization of specific antibody-forming cells in tissue sections

A new general approach has been developed for the detection of one or more different specific antibody producing cells and the simultaneous determination of their Ig isotype in tissue sections, after immunization of animals. Specificity of intracellular antibodies is demonstrated after incubation of the sections with an antigen-enzyme conjugate and the isotype of the antibodies is determined using an anti-immunoglobulin (Fc chain-specific)-enzyme conjugate followed by histochemical revelation of the two different enzymes. The principles of the method, the required antigen- and antibody-enzyme conjugates and their application in single, double or triple staining studies are reviewed. The method allows the detection of specific antibody-forming cells against protein antigens as well as against haptens. By means of haptens such as trinitrophenyl (TNP), immune responses against thymus dependent, thymus independent, and particulate antigens can be studied. In a limited number of cases the method can also be used to study the localization of antigen-antibody complexes.

Influence of carriers on the development and localization of anti-trinitrophenyl antibody-forming cells in the murine spleen

Mice were i.v. immunized with various 2,4,6-trinitrophenyl (TNP)-carrier conjugates, and the development and localization of specific (i.e. anti-TNP) antibody-forming cells (AFC) in the spleen was studied. The nature of the carrier used, thymus dependent (TD) or thymus independent type 1 or type 2 (TI-1, TI-2), had marked effects on the number and time of appearance of AFC. However, no influence of the different carriers on the localization of specific AFC in the spleen was observed. By using a double immunocytochemical technique we could simultaneously determine specificity (anti-TNP) and isotype (class and subclass) of the AFC. The TNP-carrier conjugates evoked (intracellular) immunoglobulins with carrier-characteristic isotype distribution. No carrier-dependent localization pattern, in the lymphoid compartments of the spleen, of these AFC was found. These results show for the first time the actual in situ effects of various TI and TD carriers on the development of specific AFC. Based on the present findings, no direct evidence for a special role of the marginal zone in the immune response against TI-2 antigens could be demonstrated. We suggest that this new method for in vivo investigation, in combination with existing standard enzyme- and immunohistochemical techniques, can provide more insight into the precise role of lymphoid and nonlymphoid cells in TD and TI immune responses.

TNP-enzyme conjugates for the detection of anti-TNP antibody producing cells in vivo

After injection of TNP-KLH in mice and TNP-BGG-PEN in rabbits, anti-TNP antibody-forming cells were observed in the spleen. When cryostat sections of the stimulated spleen were incubated with TNP-HRP conjugate, and then treated for HRP cytochemistry, the cytoplasm of anti-TNP-forming cells was stained red. When similar sections were incubated with TNP-AP conjugate, and then treated for AP cytochemistry, the cytoplasm of anti-TNP-forming cells was stained blue. After simultaneous incubation with TNP-AP conjugate and PEN-HSA-HRP conjugate, followed by treatment for HRP cytochemistry and AP cytochemistry, anti-TNP-forming cells with a blue cytoplasm and anti-PEN-forming cells with a red cytoplasm could be distinguished in the same spleen section.