CONTRIBUTION OF BONE MARROW CELLS AND LACK OF EXPRESSION OF THYMOCYTES IN GENETIC CONTROLS OF IMMUNE RESPONSES FOR TWO IMMUNOPOTENT REGIONS WITHIN POLY-(PHE,GLU)-POLY-PRO--POLY-LYS IN INBRED MOUSE STRAINS

Previous cellular studies on the genetic regulation of immunological responsiveness for two immunopotent regions within the branched chain synthetic polypeptide (Phe, G)-Pro--L demonstrated a direct correlation between the number of detectable immunocompetent splenic precursor cells and the response patterns of SJL, DBA/1, and F1 mice (21). In order to establish the cellular origin(s) of the genetic defect, the present study first demonstrated that thymus and bone marrow cell cooperation was required for (Phe, G)- and Pro--L-specific immune responses. Secondly, limiting dilution experiments, in which several graded and limiting inocula of marrow cells were mixed with a non-limiting number of 108 thymocytes and injected into irradiated, syngeneic recipients, indicated that the low responsiveness of the SJL and DBA/1 strains to the (Phe, G) and Pro--L specificities, respectively, could be attributed to a reduced number of precursor cells found in bone marrow. About five times more marrow precursors were detected in SJL mice for Pro--L than for (Phe, G), whereas about five times as many precursor cells were estimated for (Phe, G) as for Pro--L in the DBA/1 strain. These differences are similar to those obtained using spleen cells from unimmunized SJL and DBA/1 donors (21), and indicate that these genetically determined variations in responsiveness can be accounted for by differences in the frequencies of monospecific populations of immunocompetent cells present in bone marrow. In contrast, limiting dilution transfers of thymocytes or thymus-derived cells with an excess of syngeneic marrow cells resulted in equally frequent (Phe, G) and Pro--L responses for both SJL ad DBA/1 strains. This finding in conjunction with the observation that the generation of (Phe, G)- and Pro--L-specific responses were associated in individual recipients injected with limiting inocula of thymocytes indicated that a single population of thymocytes was stimulated by (Phe,G)-Pro--L. Therefore, it is improbable that the thymic population of immunocompetent cells contributes to expression of these genetically controlled defects

ANTIBODY RESPONSE OF INBRED MOUSE STRAINS TO ORDERED TETRAPEPTIDES OF TYROSINE AND GLUTAMIC ACID ATTACHED TO MULTICHAIN POLYALANINE OR POLYPROLINE : TYR-TYR-GLU-GLU IS A MAJOR DETERMINANT OF THE RANDOM POLY-(TYR, GLU)-POLYDLALA--POLYLYS

Five inbred mouse strains which represent high and low responders to the random synthetic polypeptide poly(LTyr,LGlu)-polyDLAla--polyLLys, designated (T, G)-A--L, to which the immune response is controlled by an H-2-linked gene, were immunized with three ordered tetrapeptides composed of tyrosine and glutamic acid attached either to multichain poly-DL-alanine or to polyproline. Only one of the three antigenic determinants, namely tyrosyl-tyrosyl-glytamyl-glutamic acid (T-T-G-G), resembled the random peptide (T, G) in the pattern of immune responses elicited against it, and in the cross-reactivity of the specific antibodies with (T, G)-A--L. The immune response pattern to the other two ordered tetrapeptides, T-G-T-G and G-T-T-G, was different from that obtained with (T, G)-A--L, and no cross-reactivity was detected between the antibodies provoked with these peptides and (T, G)-A--L. Thus, it is suggested that T-T-G-G is a major determinant in the random (T, G)-A--L

CELLULAR BASIS OF THE GENETIC CONTROL OF IMMUNE RESPONSES TO SYNTHETIC POLYPEPTIDES : I. DIFFERENCES IN FREQUENCY OF SPLENIC PRECURSOR CELLS SPECIFIC FOR A SYNTHETIC POLYPEPTIDE DERIVED FROM MULTICHAIN POLYPROLINE ([T, G]-PRO--L) IN HIGH AND LOW RESPONDER INBRED MOUSE STRAINS

SJL mice are high responders to the synthetic multichain polypeptide antigen (T,G)-Pro--L, whereas DBA/1 mice are low responders (10, 11). In order to determine whether the genetic control of immune response can be correlated with the number of antigen-sensitive precursor cells, spleen cell suspensions from normal and immunized SJL and DBA/1 donor mice were transplanted into lethally X-irradiated syngeneic recipients (incapable of immune response) along with (T, G)-Pro--L. Anti-(T, G)-Pro--L responses (donor-derived) were assayed in the sera of the hosts 12–16 days later. By transplanting graded and limiting numbers of spleen cells, inocula were found which contained one or a few antigen-sensitive precursors reactive with the immunogen. Using this method to estimate the relative numbers of such cells for the high responder SJL strain, one precursor was detected in ∼1.3 x 106 and ∼7.2 x 106 spleen cells from immunized and normal donors, respectively. In contrast, one precursor was detected in about 30 x 106 spleen cells from low responder DBA/1 mice, irrespective of whether the donors had been immunized. These results indicate that the genetic control of immunity to the synthetic polypeptide antigen investigated is directly correlated to the relative number of precursor cells reactive with the immunogen in high and low responder strains

ANTIGEN-SPECIFIC THYMUS CELL FACTORS IN THE GENETIC CONTROL OF THE IMMUNE RESPONSE TO POLY-(TYROSYL, GLUTAMYL)-POLY-D, L-ALANYL--POLY-LYSYL

The genetic control of the antibody response to a synthetic polypeptide antigen designated poly-L(Tyr, Glu)-poly-D,L-Ala--poly-L-Lys [(T, G)-A--L] has been studied in congenic high responder C3H.SW (H-2b) and low responder C3H/HeJ (H-2k) strains of mice. This response is controlled by the Ir-1 gene and is H-2 linked. The method employed was to study the ability of specifically primed or "educated" T cells of each strain to produce cooperative factors for (T, G)-A--L in vitro. Such factors have been shown to be capable of replacing the requirement for T cells in the thymus-dependent antibody response to (T, G)-A--L in vivo. The T-cell factors produced were tested for their ability to cooperate with B cells of either high or low responder origin by transfer together with bone marrow cells and (T, G)-A--L into heavily irradiated, syngeneic (for bone marrow donor) recipients. Direct anti-(T, G)-A--L plaque-forming cells were measured later in the spleens of the recipients. The results showed that (a) educated T cells of both high and low responder origin produced active cooperative factors to (T, G)-A--L, and no differences between the strains in respect to production of T-cell factors could be demonstrated; and (b) such factors, whether of high or low responder origin, cooperated efficiently with B cells of high responder origin only, and hardly at all with B cells of low responder origin. The conclusion was drawn that the cellular difference between the two strains lies in the responsiveness of their B cells to specific signals or stimuli received from T cells. As far as could be discerned by the methods used, no T-cell defect existed in low responder mice and the expression of the controlling Ir-1 gene was solely at the level of the B cells in this case

CONTRIBUTION OF DIFFERENT CELL TYPES TO THE GENETIC CONTROL OF IMMUNE RESPONSES AS A FUNCTION OF THE CHEMICAL NATURE OF THE POLYMERIC SIDE CHAINS (POLY-L-PROLYL AND POLY-DL-ALANYL) OF SYNTHETIC IMMUNOGENS

Genetic regulation of immunological responsiveness was studied at the cellular level by comparing the limiting dilutions of immunocompetent cells from spleen, thymus, and bone marrow of high and low responders as a function of the poly-L-prolyl and poly-DL-alanyl side chains of two synthetic polypeptide immunogens. The spleens of immunized and unimmunized high responder DBA/1 mice were found to contain respectively, 18- and 7-fold more limiting precursor cells specific for (Phe, G)-A--L than the spleens of SJL low responder donors. These results, using a synthetic polypeptide built on multichain poly-DL-alanine, confirm the findings reported for polypeptides built on multichain poly-L-proline (1, 2), that there is a direct correlation between immune response potential and the relative number of immunocompetent precursors stimulated. Cell cooperation between thymocytes and bone marrow cells was demonstrated for both (T, G)-Pro--L and (Phe, G)-A--L. Limiting dilutions of thymus and bone marrow cells in the presence of an excess amount of the complementary cell type indicated an eightfold lower number of detected (T, G)-Pro--L-specific precursors in DBA/1 (low responder) marrow when compared with SJL (high responder) marrow. No differences were observed in the frequency of relevant high and low responder thymocytes for the (T, G)-Pro--L immunogen. These results are similar to those reported for the (Phe, G)-Pro--L (3). In contrast to the cellular studies reported for the Pro--L series of immunogens, the marrow and thymus cell dilution experiments for (Phe, G)-A--L revealed genetically associated differences in both the marrow and thymus populations of immunocytes from high (DBA/1) and low (SJL) responders. In addition to a fivefold difference in limiting marrow cell precursors (similar to that seen in the Pro--L studies), a striking difference was observed between the helper cell activity of high responder DBA/1 and low responder SJL thymocytes. This difference was indicated by the observation that low responder thymocyte dilutions followed the predictions of the Poisson model, whereas dilutions of high responder thymocytes did not conform to Poisson statistics. Transfers of allogeneic thymus and marrow cell mixtures from DBA/1 and SJL donors confirmed the syngeneic dilution studies showing that the genetic defect of immune responsiveness to (Phe, G)-A--L is expressed at both the thymus and marrow immunocompetent cell level. The parameters presently known for genetic control of immune responses specific for (Phe, G) (Ir-1 gene) and for Pro--L (Ir-3 gene) have been compared. The Ir-1 and Ir-3 genes are not only distinct by genetic linkage tests (to H-2) (5, 6, 9), but they are also seen to be different by cellular studies. Furthermore, expression of low responsiveness within a given cell population was shown to depend on the chemical structure of the whole immunogenic macromolecule

THE ROLE OF THYMOCYTES AND BONE MARROW CELLS IN DEFINING THE RESPONSE TO THE DINITROPHENYL HAPTEN ATTACHED TO POSITIVELY AND NEGATIVELY CHARGED SYNTHETIC POLYPEPTIDE CARRIERS : CELL FRACTIONATION OVER CHARGED COLUMNS

An inverse relationship exists between the net electrical charge of immunogens and the antibodies they elicit (1). Results of an earlier study have demonstrated that the net charge phenomenon has a cellular basis, since the immune response potential of murine spleen cells to 2,4-dinitrophenyl (DNP) on a negatively charged synthetic polypeptide carrier was reduced by cell fractionation over negatively charged glass beads, whereas the response to the same hapten on a positively charged carrier was unaffected (14). To verify that the net charge correlation is expressed at the cellular level, spleen cells were fractionated over positively charged poly-L-lysine-coated glass bead columns, and their immunocompetence to DNP on positively and negatively charged carriers was tested by cell transfers in irradiated recipient mice. In this case, the fractionated cells showed reduced response potential to DNP on the positively charged carrier only. Thus, the cellular basis of the net charge phenomenon has been demonstrated for both positively and negatively charged immunogens (for the same specificity) by cell separation techniques over columns of opposite charge. In order to establish whether the cell population relevant for the charge properties of immunogens was of thymus or marrow origin, thymocytes and bone marrow cells were selectively passed over positively or negatively charged columns and mixed with unfractionated cells of the complementary type. Transfers of the filtered and unfiltered cell mixtures in irradiated recipient mice immunized with DNP on either a positive or a negative synthetic polypeptide carrier indicated that fractionation of thymocytes, but not of marrow cells, correlated with the spleen population. Thus, thymocytes fractionated over negatively charged columns and mixed with unfractionated marrow cells exhibited reduced response to DNP on the negative carrier, but normal responses to DNP on the positive carrier. The opposite result was obtained when thymocytes were passed over positively charged columns. No effect on the anti-DNP response was detected by filtration of bone marrow cells over columns of either charge. These findings indicate that it is possible to distinguish between thymocytes on the basis of their capacity to react with more acidic or more basic surfaces and that a population of thymus-derived cells may recognize immunogens on the basis of their overall electrical charge. No evidence was found by these techniques that marrow-derived cells contribute to the net charge phenomenon

THE GENETIC CONTROL OF ANTIBODY SPECIFICITY

The immune response to a synthetic polypeptide built on multichain polyproline, poly-L-(Tyr,Glu)-poly-L-Pro-poly-L-Lys [(T,G)-Pro--L], in the offspring of a cross between DBA/1 and SJL mice is under a genetic control superficially similar to the one operating for the immune response to a similar synthetic polypeptide built on multichain polyalanine, poly-L-(Tyr,Glu)-poly-D,L-Ala-poly-L-Lys [(T,G)-A--L], in the offspring of a cross between CBA and C57 mice. In both cases, the genetic control is a quantitative trait in which the major gene(s) is (are) dominant and the trait is not linked to any of the known structural genes coding for mouse immunoglobulin heavy chains. However, the genetic control of response to (T, G)-Pro--L, designated immune response-3 (Ir-3), is qualitatively different from the one operating for (T,G)-A--L [immune response-1 (Ir-1)] in that it is not linked to the histocompatibility-2 (H-2) locus. A study of the immune response to a related polypeptide built on multichain polyproline, poly-L-(Phe,Glu)-poly-L-Pro-poly-L--Lys [(Phe, G)-Pro--L], in the DBA/1 x SJL cross has shown a genetic control of antibody specificity. F1 x DBA/1 backcross anti-(Phe, G)-Pro--L sera segregate in their ability to bind (T,G)-Pro--L, and there is no linkage of anti-(T,G)-Pro--L binding capacity with the H-2s allele of the SJL grandparent. F1 x SJL anti-(Phe, G)-Pro-L sera segregate in their capacity to bind poly-L-(Phe,Glu)-poly-D,L-Ala-poly-L-Lys [(Phe, G)-A--L] and the ability to bind (Phe, G)-A--L is clearly linked to the H-2q allele from the DBA/1 grandparent. Thus, in mice all responding well to a given antigen [(Phe, G)-Pro--L], the specificity of the antibodies produced [i.e., anti-(Phe,G) or anti-prolyl] is genetically determined. Cross-inhibition of binding m (DBA/1 x SJL)F1 anti-(Phe,G)-Pro--L antisera indicates that the anti-(Phe,G) and anti-prolyl specificities are a function of two separate and largely non-crossreacting antibody populations

THE NATURE OF THE ANTIGENIC DETERMINANT IN A GENETIC CONTROL OF THE ANTIBODY RESPONSE

The response of inbred mouse strains to two polypeptides derived from multichain polyprolines, (T,G)-Pro--L and (Phe,G)-Pro--L, is different from the response of the same mouse strains to a similar series of polymers built on multi-poly-D,L-alanyl--poly-L-lysine, although the same short sequences of amino acids are attached to the side chains of the polypeptides in the two series. These results indicate that a portion of the side chain (e.g. polyalanine or polyproline) participates in the antigenic determinant. This was confirmed by studying the response of different mouse strains to two kinds of polypeptides: (T,G)-Pro-A--L 717 and 718 and (T,G)-A-Pro--L 719 and 721. Antibody assay of antisera to (Phe,G)-Pro--L with the cross-reacting antigens (T,G)-Pro--L and (Phe,G)-A-L indicates that different inbred mouse strains make antibodies specific for different parts of the same polypeptide. Thus, antibody from DBA/1 mice reacts almost exclusively with the (Phe,G) sequence, while SJL antisera bind only (T,G)-Pro--L and fail to bind (Phe,G)-A-L. The immune responses to the same amino acids on two different polypeptides (i.e. A--L and Pro--L) appear to be under separate genetic control

In Vivo Dynamical Interactions between CD4 Tregs, CD8 Tregs and CD4+CD25− Cells in Mice

BACKGROUND: Regulatory T cells (Tregs) were shown to be central in maintaining immunological homeostasis and preventing the development of autoimmune diseases. Several subsets of Tregs have been identified to date; however, the dynamics of the interactions between these subsets, and their implications on their regulatory functions are yet to be elucidated. METHODOLOGY/PRINCIPAL FINDINGS: We employed a combination of mathematical modeling and frequent in vivo measurements of several T cell subsets. Healthy BALB/c mice received a single injection of either hCDR1--a tolerogenic peptide previously shown to induce Tregs, a control peptide or vehicle alone, and were monitored for 16 days. During this period, splenocytes from the treated mice were analyzed for the levels of CD4, CD25, CD8, CD28 and Foxp3. The collected data were then fitted to mathematical models, in order to test competing hypotheses regarding the interactions between the followed T cell subsets. In all 3 treatment groups, a significant, lasting, non-random perturbation of the immune system could be observed. Our analysis predicted the emergence of functional CD4 Tregs based on inverse oscillations of the latter and CD4(+)CD25(-) cells. Furthermore, CD4 Tregs seemed to require a sufficiently high level of CD8 Tregs in order to become functional, while conversion was unlikely to be their major source. Our results indicated in addition that Foxp3 is not a sufficient marker for regulatory activity. CONCLUSIONS/SIGNIFICANCE: In this work, we unraveled the dynamics of the interplay between CD4, CD8 Tregs and effector T cells, using, for the first time, a mathematical-mechanistic perspective in the analysis of Treg kinetics. Furthermore, the results obtained from this interdisciplinary approach supported the notion that CD4 Tregs need to interact with CD8 Tregs in order to become functional. Finally, we generated predictions regarding the time-dependent function of Tregs, which can be further tested empirically in future work