Defective T-cell receptor signalling and positive selection of Vav-deficient CD4+ CD8+ thymocytes

During lymphocyte development, cellular proliferation and positive and negative selection events ensure the production of T and B lymphocytes bearing highly diverse, but self-tolerant, repertoires of antigen receptors. These processes are initiated when engagement of growth-factor receptors, or the T and B lymphocyte antigen receptors, induces tyrosine phosphorylation of specific SH2- and SH3-domain-containing cytoplasmic proteins, including Vav. Here we show that vav-/- embryonic stem cells generate only limited numbers of immature and mature T and B lymphocytes in the RAG-2 blastocyst complementation assay. Furthermore, Vav-deficient T lymphocytes showed severely impaired antigen receptor signalling. Finally, we demonstrate that Vav-dependent signalling pathways regulate maturation, but not CD4/CD8 lineage commitment, during T-cell-receptor-mediated positive selection of immature CD4+ CD8+ precursors into mature CD4+ CD8- or CD4- CD8+ T cells.

Characterization of preneoplastic thymocytes and of their neoplastic progression in irradiated C57BL/Ka mice

Mice that receive whole body split-dose irradiation develop thymic lymphomas after a long latent period. Before emergence of frank lymphomas, preneoplastic thymocytes, which are defined by their ability to progress to full malignancy on intrathymic transfer to congenic hosts, appear. A combination of mAb 1C11, which binds to a cell surface glycoprotein on lymphoma cells, and of Abs to the differentiation markers CD4 and CD8 (MHC co-receptors), and CD3 (TCR complex) was used to characterize the phenotypes of preneoplastic thymocytes and to place them within the scheme of normal T cell ontogeny. In the irradiated, preneoplastic thymus, the 1C11 molecule was found to be present on CD4-8-, CD4-8+, and CD4+8+, but not CD4+8-, cells. After intrathymic transfer to Thy-1 congenic recipients, 1C11highCD4-8- cells from irradiated mice showed the highest leukemogenic potential, followed by the 1C11highCD4-8+ and 1C11highCD4+8+ subsets. Within the 1C11highCD4-8- subset, CD3+ cells were more leukemogenic than CD3- cells. The resulting lymphomas were 1C11highCD3+4-8+ and 1C11highCD3+4+8+, phenotypes that are absent or very rare in the normal thymus, but similar to those of primary radiation-induced lymphomas. Examination of the TCR V beta repertoire in these lymphomas shows a highly significant bias, in that approximately 50% express the V beta 8 gene product. These results indicate, but do not prove, that the 1C11highCD3+4-8- cells, a very small subset of normal thymocytes, are either the target of neoplastic transformation after radiation or the earliest identifiable cell population after the transforming event. These results also suggest at least one possible pathway to define the process leading to overt lymphoma.

Characterization of preneoplastic thymocytes and of their neoplastic progression in irradiated C57BL/Ka mice

Mice that receive whole body split-dose irradiation develop thymic lymphomas after a long latent period. Before emergence of frank lymphomas, preneoplastic thymocytes, which are defined by their ability to progress to full malignancy on intrathymic transfer to congenic hosts, appear. A combination of mAb 1C11, which binds to a cell surface glycoprotein on lymphoma cells, and of Abs to the differentiation markers CD4 and CD8 (MHC co-receptors), and CD3 (TCR complex) was used to characterize the phenotypes of preneoplastic thymocytes and to place them within the scheme of normal T cell ontogeny. In the irradiated, preneoplastic thymus, the 1C11 molecule was found to be present on CD4-8-, CD4-8+, and CD4+8+, but not CD4+8-, cells. After intrathymic transfer to Thy-1 congenic recipients, 1C11highCD4-8- cells from irradiated mice showed the highest leukemogenic potential, followed by the 1C11highCD4-8+ and 1C11highCD4+8+ subsets. Within the 1C11highCD4-8- subset, CD3+ cells were more leukemogenic than CD3- cells. The resulting lymphomas were 1C11highCD3+4-8+ and 1C11highCD3+4+8+, phenotypes that are absent or very rare in the normal thymus, but similar to those of primary radiation-induced lymphomas. Examination of the TCR V beta repertoire in these lymphomas shows a highly significant bias, in that approximately 50% express the V beta 8 gene product. These results indicate, but do not prove, that the 1C11highCD3+4-8- cells, a very small subset of normal thymocytes, are either the target of neoplastic transformation after radiation or the earliest identifiable cell population after the transforming event. These results also suggest at least one possible pathway to define the process leading to overt lymphoma.

Cell cycle dependent regulation of the protein kinase TTK

TTK is a novel protein kinase detectable in all proliferating human cells and tissues. Expression of the TTK gene is markedly reduced or absent in resting cells and in tissues with a low proliferative index. In view of the apparent association between TTK gene expression and cell proliferation, we examined the regulation of this protein kinase during transit of the cell cycle. We found very low levels of TTK mRNA and protein in starved cells. When cells are induced to enter the cell cycle, levels of TTK mRNA, protein and kinase activity increase at the G1/S phase of the cell cycle and peak in G2/M. TTK mRNA levels, as well as kinase activity, drop sharply in early G1, whereas protein levels are largely maintained. TTK may play a role in cell cycle control.

IgH enhancer deregulated expression of L-myc: abnormal T lymphocyte development and T cell lymphomagenesis

Transgenic constructs containing the murine L-myc gene under the control of the immunoglobulin transcriptional enhancer element (Emu) are expressed at unexpectedly high levels in thymocytes and proliferating T cells compared with cells from bone marrow and proliferating B cells. In contrast, double transgenic animals bearing constructs containing the L- and N-myc genes similarly linked to the Emu element maintain preferential L-myc expression in T cells but express the N-myc transgene preferentially in B cells. These results indicate that the L-myc gene contains elements that act in concert with the Emu element to allow preferential expression in T lineage cells. In correspondence to the expression pattern, Emu-L-myc transgenic mice show expanded thymic cortices and irregularly formed splenic follicles with expanded T cell areas. Moreover, the percentage of thymocytes positive for the surface marker 1C11, which defines thymic progenitor cells, activated T cells and preleukemic T cells, is dramatically raised in transgenic mice compared with normal littermates. Emu-L-myc transgenic animals are predisposed to clonal lymphoid tumors, most of which are T cell lymphomas. The relative incidence, latency period, and degree of malignancy of Emu-L-myc tumors compared with Emu-N- or c-myc tumors is consistent with a lower oncogenic potential of the L-myc gene. However, the Emu-L-myc tumors do not express detectable levels of endogenous myc family genes indicating that the L-myc protein can substitute for c- or N-myc in the generation and growth of lymphoid neoplasms.

Cell type specificity and activation requirements for NFAT-1 (nuclear factor of activated T-cells) transcriptional activity determined by a new method using transgenic mice to assay transcriptional activity of an individual nuclear factor

Nuclear factor of activated T-cells (NFAT-1) is a transcription factor which is considered to be an important regulator in early T-cell activation. We have developed a system to monitor the transcriptional activity of NFAT-1 at the single cell level in whole animals. The system is based on the use of an oligomerized NFAT-1 binding motif that directs transcription of SV40 T-antigen in transgenic mice. This report represents the first demonstration that a multimerized short binding motif can function appropriately in transgenic mice. NFAT-1 activity had previously been thought to be confined to activated T-lymphocytes upon release of intracellular calcium. By targeting NFAT-1-dependent gene expression in transgenic mice we discovered new sites of NFAT-1 activity. Besides in T-lymphocytes NFAT-1 activity could also be induced in T-lymphocyte-depleted spleen cells and purified B-lymphocytes and requires agents that both release intracellular calcium and activate protein kinase C. A difference in the time course of appearance of NFAT-1 activity between T-lymphocytes and non-T-lymphocytes was revealed. Constitutive expression was observed in a small population of cells in the dermis and some mice have developed skin lesions. Interestingly, the tissue pattern of expression of the NFAT-1 activity resembles the expression pattern described for HIV-LTR/tat transgenic mice (Vogel, J., Hinrichs, S. H., Reynolds, R. K., Luciw, P. A., and Jay, G. (1988) Nature 335, 606-611). This similarity in expression and the fact that NFAT-1 has been shown to bind functional sequences in HIV-LTR suggest a role for NFAT-1 in dermal activation of the HIV-LTR.

Characterization of a rat monoclonal antibody specific for a determinant encoded by the V beta 7 gene segment. Depletion of V beta 7+ T cells in mice with Mls-1a haplotype

We have generated a rat mAb, TR310, which recognizes a determinant encoded by the murine V beta 7 gene segment of the TCR. TR310 immunoprecipitates TCR from cell lysates, co-modulates with CD3, and can be used for immunofluorescence staining of T cells. By using this antibody, we found that the average percentage of V beta 7+ peripheral T cells in Mls-1b mice was 3.8%, but only 0.8% in Mls-1a mice. A similar difference was also observed in the mature TCRhi thymocyte subsets, suggesting that V beta 7+ T cells are deleted during intrathymic maturation in Mls-1a mice. TR310 should prove to be a valuable reagent in further studies of the TCR repertoire and the analysis of factors which alter it.

Characterization of a rat monoclonal antibody specific for a determinant encoded by the V beta 7 gene segment. Depletion of V beta 7+ T cells in mice with Mls-1a haplotype

We have generated a rat mAb, TR310, which recognizes a determinant encoded by the murine V beta 7 gene segment of the TCR. TR310 immunoprecipitates TCR from cell lysates, co-modulates with CD3, and can be used for immunofluorescence staining of T cells. By using this antibody, we found that the average percentage of V beta 7+ peripheral T cells in Mls-1b mice was 3.8%, but only 0.8% in Mls-1a mice. A similar difference was also observed in the mature TCRhi thymocyte subsets, suggesting that V beta 7+ T cells are deleted during intrathymic maturation in Mls-1a mice. TR310 should prove to be a valuable reagent in further studies of the TCR repertoire and the analysis of factors which alter it.

Growth-promoting activity of IL-1 alpha, IL-6, and tumor necrosis factor-alpha in combination with IL-2, IL-4, or IL-7 on murine thymocytes. Differential effects on CD4/CD8 subsets and on CD3+/CD3- double-negative thymocytes

Many cytokines (including IL-1, IL-2, IL-4, IL-6, and TNF-alpha) have been shown to induce thymocyte proliferation in the presence of PHA. In this report, we demonstrate that certain cytokine combinations induce thymocyte proliferation in the absence of artificial comitogens. IL-1 alpha, IL-6, and TNF-alpha enhanced the proliferation of whole unseparated thymocytes in the presence of IL-2, whereas none of them induced thymocyte proliferation alone. In contrast, of these three enhancing cytokines, only IL-6 enhanced IL-4-induced proliferation. We also separated thymocytes into four groups based on their expression of CD4 and CD8, and investigated their responses to various cytokines. The results indicate that each cytokine combination affects different thymocyte subsets; thus, IL-1 alpha enhanced the proliferation of CD4-CD8- double negative (DN) thymocytes more efficiently than IL-6 in the presence of IL-2, whereas IL-6 enhanced the responses of CD4+CD8- and CD4-CD8+ single positive (SP) thymocytes to IL-2 or IL-4 better than IL-1 alpha. TNF-alpha enhanced the proliferation of both DN and both SP subsets in the presence of IL-2 and/or IL-7. None of these combinations induced the proliferation of CD4+CD8+ double positive thymocytes. Finally, DN were separated into CD3+ and CD3- populations and their responsiveness was investigated, because recent reports strongly suggest that CD3+ DN thymocytes are a mature subset of different lineage rather than precursors of SP thymocytes. CD3+ DN proliferated in response to IL-7, TNF-alpha + IL-2, and IL-1 + IL-2. CD3- DN did not respond to IL-7 or to IL-1 + IL-2, but did respond to TNF-alpha + IL-2. Finally, we detected TNF-alpha production by a cloned line of thymic macrophages, as well as by DN adult thymocytes. These results suggest that cytokines alone are capable of potent growth stimuli for thymocytes, and indicate that different combinations of these molecules act selectively on thymocytes at different developmental stages.

Growth-promoting activity of IL-1 alpha, IL-6, and tumor necrosis factor-alpha in combination with IL-2, IL-4, or IL-7 on murine thymocytes. Differential effects on CD4/CD8 subsets and on CD3+/CD3- double-negative thymocytes

Many cytokines (including IL-1, IL-2, IL-4, IL-6, and TNF-alpha) have been shown to induce thymocyte proliferation in the presence of PHA. In this report, we demonstrate that certain cytokine combinations induce thymocyte proliferation in the absence of artificial comitogens. IL-1 alpha, IL-6, and TNF-alpha enhanced the proliferation of whole unseparated thymocytes in the presence of IL-2, whereas none of them induced thymocyte proliferation alone. In contrast, of these three enhancing cytokines, only IL-6 enhanced IL-4-induced proliferation. We also separated thymocytes into four groups based on their expression of CD4 and CD8, and investigated their responses to various cytokines. The results indicate that each cytokine combination affects different thymocyte subsets; thus, IL-1 alpha enhanced the proliferation of CD4-CD8- double negative (DN) thymocytes more efficiently than IL-6 in the presence of IL-2, whereas IL-6 enhanced the responses of CD4+CD8- and CD4-CD8+ single positive (SP) thymocytes to IL-2 or IL-4 better than IL-1 alpha. TNF-alpha enhanced the proliferation of both DN and both SP subsets in the presence of IL-2 and/or IL-7. None of these combinations induced the proliferation of CD4+CD8+ double positive thymocytes. Finally, DN were separated into CD3+ and CD3- populations and their responsiveness was investigated, because recent reports strongly suggest that CD3+ DN thymocytes are a mature subset of different lineage rather than precursors of SP thymocytes. CD3+ DN proliferated in response to IL-7, TNF-alpha + IL-2, and IL-1 + IL-2. CD3- DN did not respond to IL-7 or to IL-1 + IL-2, but did respond to TNF-alpha + IL-2. Finally, we detected TNF-alpha production by a cloned line of thymic macrophages, as well as by DN adult thymocytes. These results suggest that cytokines alone are capable of potent growth stimuli for thymocytes, and indicate that different combinations of these molecules act selectively on thymocytes at different developmental stages.

An immunodominant murine lymphoma cell surface heterodimer marks thymic progenitor subsets

mAb 1C11 was raised against the cells of retrovirus-negative, radiation-induced thymomas of C57BL/Ka mice. MAb 1C11 binds to radiation- and RadLV-induced C57BL/Ka lymphomas, to lymphomas of other mouse strains and to B-lineage tumors. The 1C11 Ag is expressed on a subpopulation of normal thymocytes that is enriched in immature cells. After fractionated x-irradiation, this percentage increases gradually during the preleukemic period, hence mAb 1C11 appears to identify a transformation-related cell surface molecule. This conclusion is supported by experiments demonstrating that flow microfluorimetry-sorted, 1C11-expressing preleukemic thymocytes progress rapidly to full neoplasia following intrathymic injection, whereas nonexpressing cells do not. Most of day-14 fetal thymocytes are as strongly positive as thymic lymphomas for the 1C11 Ag whereas Ag-activated T cell lines express moderate levels. Multiparameter flow microfluorimetry analysis shows that 1C11 is expressed predominantly on CD3-/lo thymic blast cells of three phenotypically defined subsets: CD4-8-, CD4-8+, and CD4+8+, all of which contain thymic progenitors. By immunohistochemical staining, the Ag is also found in association with epithelial cells on a variety of normal, nonlymphoid tissue, but is not detectable on heart tissue. The 1C11 antibody immunoprecipitates a disulfide-linked heterodimeric protein of 85/37 kDa and the antigenic determinant is located on the H chain of the molecule. When analyzed by SDS-PAGE under nonreducing conditions, the molecule exists as a 130-kDa protein. Enzymatic digestion of the heterodimer indicates that the H chain, but not the L chain, has at least three N-linked glycosylation sites. We propose that this novel cell surface glycoprotein may be associated with processes of differentiation and lymphomagenesis.

An immunodominant murine lymphoma cell surface heterodimer marks thymic progenitor subsets

mAb 1C11 was raised against the cells of retrovirus-negative, radiation-induced thymomas of C57BL/Ka mice. MAb 1C11 binds to radiation- and RadLV-induced C57BL/Ka lymphomas, to lymphomas of other mouse strains and to B-lineage tumors. The 1C11 Ag is expressed on a subpopulation of normal thymocytes that is enriched in immature cells. After fractionated x-irradiation, this percentage increases gradually during the preleukemic period, hence mAb 1C11 appears to identify a transformation-related cell surface molecule. This conclusion is supported by experiments demonstrating that flow microfluorimetry-sorted, 1C11-expressing preleukemic thymocytes progress rapidly to full neoplasia following intrathymic injection, whereas nonexpressing cells do not. Most of day-14 fetal thymocytes are as strongly positive as thymic lymphomas for the 1C11 Ag whereas Ag-activated T cell lines express moderate levels. Multiparameter flow microfluorimetry analysis shows that 1C11 is expressed predominantly on CD3-/lo thymic blast cells of three phenotypically defined subsets: CD4-8-, CD4-8+, and CD4+8+, all of which contain thymic progenitors. By immunohistochemical staining, the Ag is also found in association with epithelial cells on a variety of normal, nonlymphoid tissue, but is not detectable on heart tissue. The 1C11 antibody immunoprecipitates a disulfide-linked heterodimeric protein of 85/37 kDa and the antigenic determinant is located on the H chain of the molecule. When analyzed by SDS-PAGE under nonreducing conditions, the molecule exists as a 130-kDa protein. Enzymatic digestion of the heterodimer indicates that the H chain, but not the L chain, has at least three N-linked glycosylation sites. We propose that this novel cell surface glycoprotein may be associated with processes of differentiation and lymphomagenesis.

Role of interleukin-4 in T-cell ontogeny: changes in cell surface phenotype and lymphokine production of immature thymocytes after culture with interleukin-4 and phorbol ester

We have analyzed the phenotype and functional capabilities of adult and fetal CD4 8 thymocytes after 4 d of culture in IL-4 and PMA. Both adult and day 14 fetal CD4 8 thymocytes failed to acquire CD4 or CD8 antigens following culture. However, changes in expression of other antigens typical of immature thymocytes were observed. For example, the frequency with which cells expressed high levels of J11d or IL-2-R was greatly decreased following culture, whereas the frequency with which high levels of MEL-14, the lymph node homing receptor were expressed were greatly increased. This phenomenon may be due to direct induction by IL-4 and PMA of MEL-14 expression on purified MEL-14lo CD4-8- thymocytes. The frequency of cells expressing CD3, Ly-1 and Pgp-1 changed only slightly. Functionally, the cultured cells produced large amounts of interferon gamma but very little IL-2 or IL-4, although freshly isolated CD4-8- thymocytes produced all three lymphokines. These results suggest that in addition to a proliferative stimulus, culture in IL-4/PMA alters the expression of several early thymocyte antigens, the functional capabilities of CD4-8- progenitor thymocytes, and may act as a selective differentiation stimulus to MEL-14lo CD4-8- thymocytes.

Functional differences and complementation between dendritic cells and macrophages in T-cell activation

Functional differences and cell collaboration between murine lymphoid dendritic cells (DC) and macrophages (M phi) in antigen presentation for T-cell activation were analysed with splenic DC and M phi, culture-derived bone-marrow (BM)-M phi, and DC-like and M phi-like cell lines. DC were the best stimulators of allogeneic mixed leucocyte reaction (MLR), but splenic M phi and small activated BM-M phi were almost as effective. In contrast to MLR stimulation, small activated BM-M phi were the most effective antigen-presenting cells (APC) for the presentation of whole Corynebacterium parvum (CP) organisms, possibly by virtue of their phagocytic and lysosomal functions, which could be particularly important for processing particulate antigens. Large activated BM-M phi were ineffective in stimulating MLR and CP-specific T-cell proliferation. The functional differences between BM-M phi subsets could not be explained by failure to express surface Ia or to take up antigen. Non-phagocytic APC, such as DC and the DC-like line P388AD.4, had low presenting activity for CP and were much less effective at presenting glutaraldehyde-fixed CP than M phi. This suggests that DC are dependent on the shedding of soluble antigen (reduced by glutaraldehyde fixation) from the bacteria, and they may also be less efficient than M phi at processing the fixed bacteria. The Ia- M phi-like line. P388D1, was devoid of APC activity, but could greatly enhance P388AD.4-induced T-cell proliferation to whole bacterial organisms. Similarly, co-culture of splenic DC and M phi produced very pronounced synergistic effects in proliferative responses to CP and keyhole limpet haemocyanin. The function of M phi n this partnership was sensitive to chloroquine and could not be replaced by M phi culture fluids or recombinant interleukin-1. Thus, M phi may contribute processed antigen in a form more suitable for presentation by DC. These results provide a rationale for the functional dichotomy between DC and M phi.

Functions of accessory cells in B cell responses to thymus-independent antigens

The functions of adherent accessory (A) cells in thymus-independent (TI) B cell activation were investigated using homogeneous A cell lines with distinct cell surface and functional characteristics, as well as inhibitors of antigen processing and interleukin 1 (IL 1) secretion. B cell responses to both type 1 and type 2 TI antigens were found to be strictly A cell dependent. Only A cells capable of IL 1 secretion could restore responsiveness in A cell-depleted spleen cells, regardless of Ia expression or antigen-processing capability. Moreover, recombinant IL 1 completely replaced A cell function in B cell responses to both TI 1 and TI 2 antigens. Finally, T cell depletion did not diminish the reconstitution by IL 1. Thus in contrast to T cell activation, IL 1 secretion is the only A cell function required in TI B cell activation, and the data are consistent with a direct role for IL 1 in B cell activation.

Functions of accessory cells in B cell responses to thymus-independent antigens

The functions of adherent accessory (A) cells in thymus-independent (TI) B cell activation were investigated using homogeneous A cell lines with distinct cell surface and functional characteristics, as well as inhibitors of antigen processing and interleukin 1 (IL 1) secretion. B cell responses to both type 1 and type 2 TI antigens were found to be strictly A cell dependent. Only A cells capable of IL 1 secretion could restore responsiveness in A cell-depleted spleen cells, regardless of Ia expression or antigen-processing capability. Moreover, recombinant IL 1 completely replaced A cell function in B cell responses to both TI 1 and TI 2 antigens. Finally, T cell depletion did not diminish the reconstitution by IL 1. Thus in contrast to T cell activation, IL 1 secretion is the only A cell function required in TI B cell activation, and the data are consistent with a direct role for IL 1 in B cell activation.

Comparative functional analysis of helper T lymphocyte responses to soluble and particulate antigens

An adaptable and sensitive assay to analyze the roles of helper T lymphocytes (TH) which recognize soluble or cell-surface bound antigens in the induction of cytotoxic T lymphocyte precursors (CTLp) is described. Long-term T cell lines that recognize purified protein derivative, keyhole limpet hemocyanin, or Corynebacterium parvum were used in these studies. The ability of T cells from these lines to induce cytotoxic T lymphocyte or antibody responses were compared with their ability to proliferate or release interleukin 2 (IL 2). The results demonstrate that these T cell lines are able to react to soluble antigen by proliferation and IL 2 release. Moreover, the same cell lines are able to interact with CTLp or with the precursors of antibody-secreting B cells to induce a response. In the induction of CTLp we observed an inverse correlation between the number of TH cells required and the concentration of antigen used to pulse the antigen presenting cells. However the correlation between the ability of TH lines to proliferate specifically in response to antigen and to act as helpers for CTLp and B cells was not absolute as cells with compromised proliferative capacity were able to efficiently deliver inductive signals.

Comparative functional analysis of helper T lymphocyte responses to soluble and particulate antigens

An adaptable and sensitive assay to analyze the roles of helper T lymphocytes (TH) which recognize soluble or cell-surface bound antigens in the induction of cytotoxic T lymphocyte precursors (CTLp) is described. Long-term T cell lines that recognize purified protein derivative, keyhole limpet hemocyanin, or Corynebacterium parvum were used in these studies. The ability of T cells from these lines to induce cytotoxic T lymphocyte or antibody responses were compared with their ability to proliferate or release interleukin 2 (IL 2). The results demonstrate that these T cell lines are able to react to soluble antigen by proliferation and IL 2 release. Moreover, the same cell lines are able to interact with CTLp or with the precursors of antibody-secreting B cells to induce a response. In the induction of CTLp we observed an inverse correlation between the number of TH cells required and the concentration of antigen used to pulse the antigen presenting cells. However the correlation between the ability of TH lines to proliferate specifically in response to antigen and to act as helpers for CTLp and B cells was not absolute as cells with compromised proliferative capacity were able to efficiently deliver inductive signals.

Heterogeneity of macrophages and dendritic cells as accessory cells

A number of different antigens was used to define the functional limits of Ia-bearing murine dendritic cells and macrophages in the processing and presentation of antigens for T cell activation. The results show considerable functional overlap as well as differences attributable to known properties of the cells. Thus both cell types could present soluble antigens up to the size of polymeric flagellin (M.W. in millions) about equally well. The nonphagocytic dendritic cells were most effective at inducing mixed leukocyte reactions in accordance with their high constitutive level of Ia expression. On the other hand, splenic macrophages were three to nine times better than dendritic cells at presenting particulate, heat-killed Corynebacterium parvum organisms to T cells lines, and small activated macrophages from bone marrow cultures were three times better again than splenic macrophages. Large activated bone marrow macrophages were not effective antigen presenters probably because of nonspecific suppression. These observations are consistent with the phagocytic and lysosomal activities of macrophages that enable them to ingest and process particulate antigen efficiently. Nevertheless, the capacity of dendritic cells and the dendritic-like line, P388.AD.4, to present particulate bacterial antigens suggests that these cells could either do the processing extracellularly or pick up soluble antigenic moieties shed from the bacteria and antigen processing macrophages. Glutaraldehyde fixation of C. parvum presumably stopped antigen shedding, since it produced a greater reduction of the T cell response with dendritic cells and P388.AD.4 as presenting cells than with macrophage presenters. Alternatively, the fixation could make the bacteria less "digestible" to dendritic cells than to macrophages. More characterization of the fate of antigens following encounter with accessory cells is necessary to distinguish between these possibilities.

A comparison of the stimulatory activities of lymphoid dendritic cells and macrophages in T proliferative responses to various antigens

The identities of murine accessory cells and the mechanism by which they process antigen and stimulate T cell proliferation have been examined with cell separation techniques and specific agents to block antigen catabolism. Using preparations of splenic dendritic cells (DC) and macrophages (M phi) with minimal cross-contamination, we found that only DC could induce syngeneic mixed leukocyte reaction (MLR), whereas both DC and M phi could initiate allogeneic MLR. This observation may have significant implications for syngeneic MLR as a manifestation of self Ia recognition, and for the cell type that defines self Ia during ontogeny. DC and M phi could present soluble antigens such as purified protein derivative of tuberculin (PPD) and Salmonella flagellin about equally well to antigen-specific T cell lines. M phi, however, were much more effective than the non-phagocytic DC at inducing T cell proliferation to whole Corynebacterium parvum organisms. These differences could not be attributed to differences in antigen uptake. The results suggest that the bacteria must be ingested and processed by phagocytes before T cell activation. Using the lysosomotropic agent chloroquine to inhibit antigen catabolism in accessory cells, we found that the presentation of large antigens by M phi and DC was abolished by chloroquine treatment, whereas T cell activation by antigens (such as PPD or integral membrane Ia for MLR) that apparently required no processing was relatively insensitive to chloroquine. Thus, in addition to differences between cells, discrete functions within each cell type can also be distinguished.

A comparison of the stimulatory activities of lymphoid dendritic cells and macrophages in T proliferative responses to various antigens

The identities of murine accessory cells and the mechanism by which they process antigen and stimulate T cell proliferation have been examined with cell separation techniques and specific agents to block antigen catabolism. Using preparations of splenic dendritic cells (DC) and macrophages (M phi) with minimal cross-contamination, we found that only DC could induce syngeneic mixed leukocyte reaction (MLR), whereas both DC and M phi could initiate allogeneic MLR. This observation may have significant implications for syngeneic MLR as a manifestation of self Ia recognition, and for the cell type that defines self Ia during ontogeny. DC and M phi could present soluble antigens such as purified protein derivative of tuberculin (PPD) and Salmonella flagellin about equally well to antigen-specific T cell lines. M phi, however, were much more effective than the non-phagocytic DC at inducing T cell proliferation to whole Corynebacterium parvum organisms. These differences could not be attributed to differences in antigen uptake. The results suggest that the bacteria must be ingested and processed by phagocytes before T cell activation. Using the lysosomotropic agent chloroquine to inhibit antigen catabolism in accessory cells, we found that the presentation of large antigens by M phi and DC was abolished by chloroquine treatment, whereas T cell activation by antigens (such as PPD or integral membrane Ia for MLR) that apparently required no processing was relatively insensitive to chloroquine. Thus, in addition to differences between cells, discrete functions within each cell type can also be distinguished.