Rabbits possess conventional T lymphocytes

A concept of immune regulation of somatic cell differentiation

On the basis of several lines of experimental evidence a hypothesis is advanced on autoimmune regulation of somatic cell differentiation in an immunologically mature organism ("self-anti-self" hypothesis of differentiation). There are supposed to be clones of lymphocytes interacting via their antigen-recognizing receptors with autologous differentiation antigens on various target cells. This interaction would modify the genetically determined rate of cell differentiation. Some implications of the hypothesis are discussed in relation to immunological memory, tolerance etc. In particular, the new concept might imply similarity (or identity) of the genes coding for autologous differentiation antigens and those responsible for the idiotypes of antigen-recognizing lymphocyte receptors.

Fine-specificity of the lambda and chi L chains associated with antibodies directed to alpha (1 leads to 3) glucosyls in dextran

The function of BALB/c primary B precursors, responding to dextran (dex) B-1355, and the fine-specificity of the B-1355-binding, lambda and chi, monofocal antibody (Ab) generated by the precursors have been examined. In splenic fragments from Limulus polyphemus haemocyanin (LPH)-primed, lethally irradiated, euthymic or nu/nu BALB/c mice cultured with thymus-independent (TI) dex B-1355, B-1355-lipopolysaccharide (LPS), B-1355-LPS-LPH, or thymus-dependent (TD) dex B-1355-LPH, the lambda 1 precursors responded with B-1355-binding Ab substantially equally with respect to precursor frequency, rate of Ab production, and range of fine-specificity, but not with respect to frequency of the IdX and IdI isotypes related to the VH and DH associated with the lambda 1. The lambda 2 contributed minimally to the repertoire. The chi precursors responded with B-1355-binding Ab at a rate nearly equal to the lambda 1 only under TD stimulus in euthymic fragments. A comparison of the lambda 1 and chi Ab fine-specificity, by inhibition of binding with dex differing in epitope contents and configurations, showed marked restriction in the chi relative to the lambda 1. Only approximately 10% of the relatively more abundant chi TD response showed fine alpha (1 leads to 3) specificity similar to that of the lambda 1. The lambda 1 fine-specificity diversity resided mainly in the IdI fraction.

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 effect of temperature-dependent autorosettes on B/T cell ratios of purified rabbit peripheral blood lymphocytes

Contradictory reports as to B/T cell ratios in the peripheral blood lymphocytes (PBL) of rabbits led to an investigation of current purification methods. PBL prepared by sedimentation at 37 degrees C in gelatin solution showed the same B/T ratios as did whole blood. PBL prepared by the Ficoll-Hypaque method at 4 degrees C or at room temperature were enriched in B cells compared to the whole blood. This enrichment depended on the presence of autologous erythrocytes during centrifugation and it was not demonstrable when centrifugation was carried out at 37 degrees C. Resuspended red cell pellets contained more than 3 times as many rosette-forming cells if the pellets were obtained by centrifugation of blood on Ficoll at 4 degrees C rather than 37 degrees C. We, therefore, conclude that aggregation of T cells with autologous erythrocytes is responsible for the depletion of B cells in the PBL prepared by the Ficoll-Hypaque method at 4 degrees C or at room temperature.

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

Rabbit peripheral blood lymphocytes (PBL) were analyzed by immunofluorescence using anti-T cell conjugates and anti-Fab, anti-a1 allotype, anti-IgM and anti-IgA conjugates. In addition, T cells were demonstrated by rosetting with papain-treated homologous erythrocytes. Control experiments, using acid treatment and incubation at 37 degrees C for 18 h after or without pronase treatment, revealed the endogenous origin of all surface determinants tested. A good correlation was found between results obtained with the two anti-T cell conjugates used and the T rosette test on PBL and on lymphoid cells isolated from various organs. In lymphocytes isolated from peripheral blood and from various lymphoid organs, the percentages of T and B cells were respectively 45 and 38 for PBL, 10 and 46 for bone marrow, 27 and 31 for appendix, 40 and 45 for spleen, 42 and 46 for Peyer's patches, 96 and 0.3 for thymus and 70 and 16 for peripheral lymph nodes. The percentage of "null" cells in lymphocyte populations derived from bone marrow and appendix is rather high. The final percentages of T and B cells in rabbit PBL depend to a significant extent on the method of isolation, especially isolation by Ficoll-Hypaque centrifugation results in a depletion of T cells. Moreover, a rather impure lymphoid cell suspension is obtained. In double incubation experiments, T cells (as defined by T cell antigen(s) or rosette formation) and B cells (Fab-bearing cells) were entirely different subpopulations. Allotypes of the a locus could not be detected on the surface of T cells. The results are discussed with respect to genetic coding of antigen receptors on B and T cells.

Regulation of tumor growth and antibody clone expression by antigen and anti-idiotype antibody ligands with specificity for receptor-binding sites

Dextran ligands, modified to increase epitope reactivity with receptors, were more effective in suppressing BALB/c mouse plasmacytomas MOPC 104 E and J-558, which bind alpha (1 leads to 3) dextran and have an idiotype (Id) in the common, than autoantibody (Ab) against the Id unique to each of the proteins secreted by the two tumors (the (IdI). BALC/c immunized with 104 E myeloma protein and expressing an antibody response to the 104 E IdI exhibited a specific, anti-104 E IdI transplantation resistance to lethal grafts of 104 E, but not J-558, tumors notwithstanding the shared common Id and similar ability to bind alpha(1 leads to 3) dextran. This autoantibody did not prevent modulation of the 104 E tumor to variant forms or the growth of the variants. On challenge with alpha (1 leads to 3) dextran, the immunized mice expressing the anti-104 C IdI responses failed to express the 104 D IdI-like antibody clone present in the normal, anti-alpha (1 leads to 3) dextran antibody repertoire. Passive, iso-anti-104 E IdI antibody had a transitory suppressive effect on the normal, 104 E IdI-like antibody clone but failed to circumvent 104 E tumor growth. It is apparent that the greater effectiveness of ligands strongly reactive in a nonphysiological manner with the tumor receptors lies in the stabilization of the tumor load without inducing variant escape or a disturbance of the immune network, and that receptor expression and malignancy state are not necessarily co-extensive functions.

Purification of rabbit B spleen cells by removal of adherent and of T cells

B lymphocytes from the rabbit spleen were freed of T cells by removal of cells which formed rosettes with papain-treated rabbit erythrocytes. Additional purification could be achieved if fractionation by rosette removal was preceded by removal with a magnet of cells which adhered to or ingested poly L-lysine coated iron core particles. Cell yield and purification were assessed by complement mediated cytotoxic kill of B and T cells with antibody directed against RABELA and RTLA, respectively. Other criteria depended on determination of the number of Fc receptor bearing cells and of thymidine uptake by cells which were stimulated with concanavalin A, PHA or with antibody directed against the allotypic specificity of receptor Ig light chains. Purified preparations of B cells were obtained in a yield of about 20% of the B cells in the original spleen and contained less than 10% of cells which were not B cells. This method allows purification which does not interfere with the membrane of the isolated cells.

A simple technique for testing the in vitro response of rabbit lymphocytes to PHA and allogeneic cells

Lymphocytes of rabbits can be separated from small quantities of heparinized whole blood using a simple density gradient of Ficoll-Ronpacon 1.09. This separation technique yields a pure suspension of viable cells allowing reproducible results from cultures stimulated either with PHA or allogeneic lymphocytes isolated by the same technique.

Purine nucleoside phosphorylase in lymphocytes of various mammalian species

The distribution of purine nucleoside phosphorylase has been assessed by light and electron microscopy in peripheral lymphocytes of man, the rabbit, rat, mouse, guinea-pig, pig and dog. The enzyme activity was detected in the cytosol of the majority of lymphocytes in all species. The amount of reaction product was high in the rabbit, man, guinea-pig and dog, mpderate in the rat and very low in the pig and mouse. Other blood cell types are reactive as well, although there is a variation between species. A possible relationship of purine nucleoside phosphorylase with particular subpopulations of lymphocytes is suggested.