Surface Ig on rabbit lymphocytes. Rabbit B and T cells are distinct populations

A morphological and immunohistological study of the human and rabbit appendix for comparison with the avian bursa

Diversification of the primary antibody repertoire occurs in young rabbit appendix. As a prelude to molecular investigation of whether human appendix has a similar role, we compared the lymphoid morphology and distribution of common B- and T-cell subsets in frozen and/or paraffin-embedded normal appendix specimens at various ages. IgA, IgM and IgG staining patterns were similar in frozen human and rabbit appendices. The elongated follicles of the young human and rabbit appendices regressed with age to resemble Peyer's patches. Although similar in morphology to the bursa, human and rabbit appendix follicles differ in that they do not involute completely with age and contain significant numbers of germinal center (GC) T cells although the number is low early in life. If the human appendix functions as a primary lymphoid organ, it may occur during the first few months of age when the GC T-cell density is low.

A study of the proliferative response of rabbit T cells using the BrdU-Hoechst method

Con-A- and PHA-induced proliferation of cells from rabbit thymus, spleen and mesenteric lymph node was studied with the DNA-fluorescent probe 33258 Hoechst. The fluorescence of this probe is quenched when 5-bromo-2'-deoxy-uridine is incorporated into nascent DNA during the S phase. Fluorescence decreased with increasing content of newly formed DNA per cell. Proliferation kinetics and the number of Con-A- and PHA-reactive cells (C+ and P+ cells) were determined cytofluorometrically . Lymphocytes from control and dexamethasone (DX)-treated animals start their proliferation early: after 42 hr about 25% of the control and the majority of the DX-resistant cells finished their second cell division. Small numbers of C+ (12.0%) and P+ (3.5%) cells were found in control thymus, while these percentages were enhanced in DX thymus: 32.5 and 27.0% respectively; 50% of the spleen T cells in control and DX animals are C+ or P+ and 75% of the lymph-node T cells are C+ (after DX 45%) and 50% are P+ (after DX also 50%). It is concluded that in thymus and lymph nodes, a steroid sensitive (Ss) C+P-, and in lymph nodes a Ss C+P+ cell pool is present. A mitogen non-proliferative cell pool (C-P-) is present in control and DX thymus.

Different T cell antigens and receptors for peanut agglutinin and Helix pomatia agglutinin on steroid-sensitive and resistant lymphocytes in the rabbit using double immunofluorescence

Rabbit T lymphocytes were characterized using fluorochrome-labelled antisera against thymus cell determinants and fluorochrome-labelled lectins. Three anti-T cell antisera were used, detecting different antigenic determinants on the majority of T cells. Only small subpopulations were found stained by one of the three antisera. After dexamethasone (DX) treatment, the proportion of T cells was significantly increased in bone marrow and appendix, presumably by different mechanisms. Cells binding peanut agglutinin, mainly belonging to the T cell population, were present in small numbers in thymus, spleen, lymph node, and appendix from normal as well as from DX-treated animals. In bone marrow, however, a large PNA+ population showing neither T nor B cell surface properties was observed. After treatment with neuraminidase (NA), PNA binding sites were exposed on B as well as on an increased number of T cells. It is suggested, therefore, that T and B cells retained their PNA receptors during maturation. Masking of these receptors will take place before differentiation of T cells is initiated within the thymus. After NA treatment, also binding sites for Helix pomatia agglutinin were exposed on T cells and to different extents, revealing subsets of negative, weakly and strongly positive HPA cells. HPA weakly positive cells form the major population present in the thymus, while HPA strongly positive cells constitute the major population of the T cells in spleen and lymph node. The exposure of receptors for PNA of HPA appears not to be related to the steroid sensitivity of the cells.

Differentiation antigens identify subpopulations of rabbit T and B lymphocytes. Definition by flow cytometry

A panel of six monoclonal antibodies produced against cell surface glycoproteins of a rabbit T lymphocyte line was used with flow cytometry to define rabbit lymphocyte subpopulations. Four thymocyte populations were characterized by size and expression of cell surface antigens and appear to represent stages in thymocyte differentiation. Rabbit spleen contained five subpopulations: two of T lineage, two of B, and a null cell subset. Bimodal distribution of staining of thymocytes and peripheral T cells was observed using an antibody (9AE10) directed against a Thy-1 analogue in the rabbit, suggesting two separate T cell lineages. One of the monoclonal reagents, L11/135, reacted strongly with peripheral rabbit T cells as shown by two-color immunofluorescence. In functional studies, only the L11/135-bearing cells responded to the T cell mitogens concanavalin A and phytohemagglutinin and to allogeneic splenocytes. The thymocyte subpopulations and the peripheral T and B cell subsets differ from those described in mouse and man.

Effects of anti-Ig reagents on T cell functions I. Activation of rabbit T cells by anti-allotype antibodies

Rabbit lymphocytes were analyzed by flow microfluorometry, using anti-T cell and anti-Ig reagents. Rabbit T cells and cells expressing surface Ig (B cells) appeared to belong to distinct subpopulations which could be separated on the basis of their selective adherence to nylon wool columns or to anti-Ig-coated dishes. Using flow microfluorometry, no evidence was obtained for the expression of a allotypes (VH framework) on T cells. Separated lymphocyte populations were functionally characterized using an in vitro proliferation assay. B and T cells from rabbit spleen or peripheral blood responded in a differential fashion to B and T cell-specific mitogens and to anti-Ig antibodies. Although such T cells did not respond upon stimulation with anti-Ig antibodies alone, significant proliferation could be induced by simultaneous addition of anti-Ig and T cell growth factor. In addition, activated T cells, derived from lymph nodes of immunized rabbits, generated a proliferative response upon stimulation with anti-Ig reagents alone. The above-mentioned effects on T cells could be obtained using heterologous anti-Ig antibodies or isologous anti-allotype antibodies, directed either against a allotypes (VH framework) or against b allotypes (kappa light chain). Antibodies against the Fc portion of rabbit Ig or against irrelevant allotypic specificities were ineffective in triggering T cells. Fab fragments from anti-allotype antibodies were equally stimulatory for T cells as compared to intact IgG, indicating that cross-linking of Ig-like molecules is not a necessary requirement for anti-Ig-induced T cell activation.

Immunoglobulin VH determinants defined by monoclonal antibodies

Hybridoma clones secreting antibodies against common VH determinants were readily produced by fusion of cells from mice immunized with isolated V mu fragments of human immunoglobulins (Ig), but not with intact Ig molecules or isolated heavy chains. Four monoclonal antibodies to the V mu fragments of different IgM paraproteins were selected for analysis: MH-44 (mu kappa), GB-24 (mu kappa), NF-11 (gamma 1 kappa), and SA-44 (gamma 1 kappa). Each antibody reacted with the homologous V mu fragment, homologous mu chain, and normal gamma chains, but not with the intact IgM molecules, intact IgG, or isolated light chains, as determined by radioimmunoassay. The VH reaction spectra with a panel of myeloma heavy chains showed overlapping but distinctive patterns for the four antibodies. Each of the four monoclonal anti-VH antibodies appeared to react with a different "hidden" VH determinant that is not exposed on undenatured, intact Ig molecules and differs from conventional VH subgroup determinants. In immunofluorescence studies, the monoclonal anti-VH antibodies did not bind to surface Ig on viable B lymphocytes, but visibly stained subpopulations of fixed B lymphocytes, pre-B cells, and normal plasma cells. The mean frequencies of VH+ plasma cells were 30% (MH-44), 17% (GB-24), 13% (NF-11), and 3% (SA-44), and similar frequencies were obtained for the VH+ B cell subpopulations. While subpopulations of B cells could be identified at all stages in differentiation by immunofluorescence with the anti-VH antibodies, neither resting nor activated T cells expressed these VH determinants in detectable amounts.

The use of tannic acid fixation for the electron microscope visualization of fluorochrome-labelled antibodies attached to cell surface antigens

Tannic acid as a prefixative for EM purposes was introduced by Futaesaku et al. (1972). The fixative creates conditions for enhancing electron density of different protein materials. By using a mixture of tannic acid and glutaraldehyde as prefixative, followed by a routine procedure of postfixation (OsO4) and poststaining (uranylacetate and lead citrate), membrane bound antibodies not conjugated with electron dense markers are made visible under the electron microscope.

Surface immunoglobulin of rabbit peripheral blood lymphocytes: detection of allotypes by fluorescence and rosetting

Specific anti-allotype reagents were prepared to detect heavy and light chain allotypes on surface immunoglobulin-positive (sIg+) cells from a3a3b4b4, a2a2b5b5 homozygous and a2a2b4b5 heterozygous rabbits. Total sIg+ peripheral blood lymphocytes (PBL) were detected with fluorescein-labeled goat anti-light chain and sheep anti-rabbit Ig reagents. The total sIg+ cells detected with these reagents and the sum of a and b allotypes individually measured with specific fluorescent anti-allotype reagents (a2 + a3 or b4 + b5) were measured more or ess the same when measured by fluorescence-activated cell sorter (FACS) II flow microfluorometry. The data provided no evidence for single cells expressing both allelic allotypes (allelic inclusion). We found that FACS and resetting techniques were generally equally sensitive. However, we detected a greater proportion of total b4+ plus b5+ cells by rosetting than by fluorescence in some PBL preparations from heterozygous b4b5 rabbits. This was not seen with artificial mixtures of b4b4 and b5b5 cells. The nature of these cells is not yet known. Conceivably, they were not scored as lymphocytes by light-scatter analysis on the FACS and hence were not counted, but were indistinguishable from lymphocytes by microscopy.

Idiotypic lymphocytes in the rabbit: occurrence and nature of idiotypic lymphocytes in normal and hyperimmunized rabbits

Rabbits were hyperimmunized with Micrococcus Pysodeicticus, leading to homogeneous antibody responses. Peripheral blood lymphocytes were taken from the rabbits before and monthly (during 3 months) after the start of the immunization. The cells were stored frozen. Lymphocytes were tested with anti-idiotypic conjugates for the presence of surface idiotypic structures. The nature of the idiotype-positive cells was determined with respect to the presence of IgM or T-cell antigenic determinants on their surface. A sharp rise and fall in the percentage of idiotypic lymphocytes was found, ranging between 1/40,000 and 1/1,000. Initially almost all idiotypic lymphocytes were IgM-positive. In the blood taken 2 months after the start of the immunization 20% of the idiotypic cells belonged to the T-cell population and 10% were negative for both IgM and T-cell antigenic determinants.

Fc receptors on rabbit lymphocytes. Existence of receptors for IgG antibody complexed with antigen; conditions for its detection

The presence of Fc receptors (FcR) on rabbit peripheral blood leukocytes is demonstrated using rosette formation with an ox erythrocyte-antibody (EoxA) complex. The receptor is specific for the Fc fragment of IgG (neither IgM nor F (ab')2 anti-Eox mediates rosette formation) that is antigen-bound (aggregated rabbit IgG inhibits the rosette formation only transiently). The receptor is species-specific: guinea pig IgG/Eox, goat IgG/Eox and sheep IgG/Eox complexes do not show rosette formation, and goat IgG aggregates do not inhibit rosette formation. The origin of the target erythrocytes is of importance. Sheep erythrocytes are not useful, and within Eox large differences between donors were found. Rosette formation was only inhibited by pretreatment of the rosette-forming cells with homologous immune complexes, whereas the size of the antigen greatly influenced the degree of inhibition. The rabbit FcR is pronase-resistant, unlike the human and murine RcR. The interaction of IgG and the FcR is not inhibited by isolated C gamma 3 domains. Further evidence for the requirement of the whole Fc region was obtained in experiments where inhibition of the rosette formation was observed using antisera directed to the C gamma 3 and the C gamma 2 domain, respectively. Anti-Fab antiserum did not inhibit rosette formation. Results are discussed in relation to the mechanism of allotypic suppression.

Fc receptors on rabbit lymphocytes. Identification and organ distribution of rosette-forming cells; cocapping with surface immunoglobulin

Fc receptor (FcR)-bearing cells were demonstrated using ox erythrocytes coated with homologous IgG-type antibodies (EA gamma) in rabbit peripheral blood leukocytes (PBL) and in various lymphoid organs. Discrimination of the rosette-forming cells (RFC) is carried out after prior ingestion of tetramethylrhodamine isothiocyanate-labeled latex particles and in transmission electron microscopic studies. Most of the nonlymphoid cells (5-10%) in PBL and spleen cell suspensions expose FcR. These nonlymphoid cells are almost absent in other lymphoid organs, except in bone marrow. The average percentage of cells rosetting with IgG-sensitized erythrocytes (EA gamma RFC) in lymphoid cell preparations of the various tissues was as follows: PBL 25%, bone marrow 65%, appendix 37%, spleen 40%, Peyer's patches 44%, thymus 2% and peripheral lymph node 27%. The nature of FcR-bearing PBL was further studied using F (ab')2 anti-IgM, anti-IgA or anti-T cell conjugates. About half of the population of B cells, bearing IgM or IgA express FcR. Moreover, about 80% of the RFC are found within the B cell population. Only a few T cells were found rosetting with EA gamma suggesting that most of the non-B lymphoid RFC are "null" cells. In different lymphoid organs, the percentages of EA gamma RFC and B cells are comparable but not identical A greater part of the EA gamma RFC also expresses the receptor for the third component of complement. After capping of membrane IgM determinants, FcR is located in the same cap on the majority (60%) of the FcR-positive IgM-capped cells.