Regulation of interleukin 2 receptor expression by interleukin 2

Immunophenotypic patterns of T-cell activation in neuroinflammatory diseases

OBJECTIVES

We aimed to gain insights into the pathogen-specific differences in early adaptive immune responses following central nervous system infections with Borrelia burgdorferi and viral pathogens by studying the immunophenotypic patterns of T-cell activation. Moreover, we wished to determine whether the expression of T-cell activation markers reflects disease activity in multiple sclerosis (MS).

METHODS

Proportions of cerebrospinal fluid T-cells expressing the markers HLA-DR, CD25 and CD38 were determined in patients with MS (n = 40), acute viral meningomyeloradiculoneuritis (VID, n = 26), early neuroborreliosis (NB, n = 23) and non-inflammatory neurologic diseases (n = 51) by using flow cytometry. In relapsing-remitting MS, disease activity was assessed by clinical examination and magnetic resonance imaging.

RESULTS

For each of the surface markers that were examined, significant differences in T cell proportions were found between patient groups. The proportion of HLA-DR+ T cells was higher and that of CD25+ T cells lower in NB compared with VID. These differences were attributable only to the early phase of the disease (< or = 6 days after symptom onset). Among MS patients, there was a trend for higher proportions of T cells expressing activation markers in patients with gadolinium-enhancing lesions.

CONCLUSIONS

The decreased CD25 expression in NB may reflect immunomodulatory effects of B. burgdorferi facilitating persistent infection. Larger prospective studies of T-cell activation markers for ascertaining the association between cellular markers and clinical surrogates of disease activity in MS are warranted.

Mouse langerhans cells differentially express an activated T cell-attracting CC chemokine

Epidermal Langerhans cells represent an immature population of dendritic cells, not yet able to prime naïve T cells. Following in vitro culture Langerhans cells mature into potent immunostimulatory cells. We constructed a representative cDNA library of in vitro matured murine Langerhans cells. Applying a differential screening procedure 112 differentially expressed cDNA clones were isolated. Thirty-six clones represented cDNA fragments of the same gene, identifying it to be the most actively expressed gene induced in maturing Langerhans cells. A full-length cDNA was sequenced completely. The open reading frame codes for a protein of 92 amino acids containing a leader peptide of 24 amino acids, yielding a mature protein of 7.8 kDa molecular weight. Database searches revealed 99.4% sequence identity on the nucleotide level to the recently described mouse CC chemokine ABCD-1, as well as 74% sequence identity to the human CC chemokine, the macrophage-derived chemokine/stimulated T cell chemotactic protein. Expression was analyzed by reverse transcriptase-polymerase chain reaction on a large panel of cell types. Unlike the macrophage-derived chemokine, expression was not detected in macrophages stimulated by various cytokines. Expression is restricted to cultured Langerhans cells, in vitro cultured dendritic cells, and lipopolysaccharide-activated B cells. Recombinant protein was expressed in the yeast Pichia pastoris and purified to homogeneity. Whereas no chemotactic activity was observed in chemotaxis assays for naïve T cells, B cells, cultured dendritic cells, and Langerhans cells, a strong chemoattractant activity was exerted on activated T cells. Thus, production of this chemokine by dendritic cells may be essential for the establishment and amplification of T cell responses.

The Actin-Bundling Protein Fascin Is Involved in the Formation of Dendritic Processes in Maturing Epidermal Langerhans Cells

Dendritic cells (DC) are characterized by their unique potential to prime naive T cells. Epidermal Langerhans cells (LC), the DC resident in the epidermis, gain this immunostimulatory capacity following Ag contact in vivo or during in vitro culture of epidermal cell suspensions. To analyze differential gene expression in maturing LC, we constructed a highly representative cDNA library of cultivated LC (cLC) in λ ZAP II containing 18 × 106 independent clones. This library was screened with freshly isolated Langerhans cell (fLC)- and cLC-derived probes for cLC-specific cDNAs. The cDNAs identified were sequenced and analyzed by database searches. Two cDNA fragments were identified as fragments of fascin, indicating that fascin is differentially expressed in LC. By competitive RT-PCR, we confirmed that fascin is highly expressed in cLC cultivated for 1, 2, and 3 days, while no signals were obtained with fLC. Western blot and immunofluorescence analysis revealed cLC-specific expression of fascin on the protein level as well. Fascin is known to be involved in the organization of the actin cytoskeleton in cytoplasmatic extensions of nerve growth cones. Its differential expression in maturing LC coincides with the formation of numerous dendritic projections in LC. Their formation was inhibited by incubation of LC with fascin antisense oligonucleotides during cultivation. Therefore, we conclude that fascin is necessary for the formation of the dendritic processes of maturing Langerhans cells and may thus influence T cell-LC interaction.

Genetic control of interleukin-2-like activity is distinct from that of mitogen response in chickens

Two genetic model systems, consisting of a series of sublines differing in linkage between the B blood group (Ea-B) and a gene that encodes immune response to glutamic acid-alanine-tyrosine (Ir-GAT) and a series of highly inbred lines of chickens, were used to examine the relationship between genetic control of levels of interleukin-2-like (IL-2-like) activity and genetic control of mitogen response to concanavalin A (Con A). Results obtained by using the highly inbred lines suggested that levels of IL-2-like activity were associated with levels of mitogen response to Con A. Results obtained by using the Ea-B/Ir-GAT sublines, however, suggested that levels of IL-2-like activity were not associated with the mitogen response to Con A. Levels of IL-2-like activity were associated with Ea-B but not with Ir-GAT, whereas the mitogen response to Con A was associated with both. High levels of IL-2-like activity were demonstrated in birds that had low levels of mitogen response to Con A. Previous genetic events that have occurred within these sublines may have resulted in the dissociation of genetic control of levels of IL-2-like activity and the response to the blastogenesis-inducing mitogen. This demonstrates the independence of genetic control of IL-2-like activity from that of proliferative response to the inducing mitogen.

Associations of genetics and sampling time with levels of interleukin-2 activity

The interleukin-2 (IL-2) assay has become a useful tool for examining the cellular immune response. Because of a lack of avian IL-2-dependent cell lines, the avian IL-2 assay in its present state, however, is not currently as powerful as its mammalian counterpart in effectively evaluating levels of IL-2 activity. The use of an avian IL-2 reference standard, Percoll-enriched populations of lymphoblasts, and sample collection times were examined to optimize the assay for comparing levels of IL-2 activity in a large number of birds. The reference standard was effective in accounting for assay-to-assay variance. Percoll-enriched populations of responding lymphoblasts were more sensitive to IL-2 than nonseparated populations of cultured peripheral blood lymphocytes. Levels of IL-2 activity of cells isolated from the same bird did not change within a 1-week period, although differences did approach significance. In addition, levels of IL-2 activity differed between genetically distinct populations.

Involvement of soluble mediator(s) different from interleukin (IL) 1 in the antigen-induced IL 2 receptor expression and proliferation of L3T4+ (CD4+) T lymphocytes

Proliferation of T lymphocytes (T cells) requires the interaction of interleukin 2 (IL 2) with the high affinity form of the IL 2 receptor (IL 2R). IL 2 production as well as IL 2R expression are generally induced simultaneously in T cells by the recognition of specific antigen displayed on the surface of syngeneic antigen-presenting cells. The experiments described herein show that the expression of IL 2R has different requirements than the production of IL 2 (and other lymphokines). Stimulation of antigen-specific L3T4+ T cell lines with antigen-pulsed spleen cells (SC) treated with ultraviolet (UV) light results in efficient IL 2 production but only minimal proliferation due to reduced IL 2R expression, as compared to T cells stimulated by antigen and SC without UV light treatment. The reduced IL 2R expression/proliferation correlates with the absence of a soluble mediator(s) termed T cell-stimulating factor (TSF) in the supernatants of T cells stimulated with antigen-pulsed, UV light-irradiated SC. Addition of TSF of these T cells could at least partially restore the proliferative response or enhance IL 2R expression. Because TSF is present in the supernatant of T cells triggered by antigen and SC but is absent when the latter are UV light treated, we suggest that TSF is a product of metabolically active splenic antigen-presenting cells. The macrophage products interleukin 1 alpha + beta as well as some other cytokines show no TSF activity.

Differential regulation of interleukin 2 (IL-2) receptor expression on antigen-specific human T cell clones by IL-2

A panel of human T cell clones bearing exclusively the T4 (helper) phenotype and demonstrating specificity to a well-characterized soluble glycoprotein antigen (185,000 dalton streptococcal antigen, SA) is described. After having been cultured in exogenous interleukin 2 (IL-2) for 7 days in the absence of the specific antigen, two of the clones, namely SA1.4 and SA1.23, show stronger proliferative responses to the ligand as compared to the other T4 clones. Analysis of both the high- and low-affinity IL-2 receptor (IL-2R) levels reveals that IL-2 mediates differential regulation of high affinity IL-2R expression on these antigen-deprived cloned cells. Higher levels of surface expression of the IL-2 binding sites on SA1.4 and SA1.23 as compared to the other clones are observed throughout the 7-day culture period that these lymphocytes are maintained in exogenous IL-2. All the cloned cells appear to have returned to their "unstimulated states" as noted by their stable low expressions of Tac antigen and high affinity IL-2R. The unstimulated states of SA1.4 and SA1.23 are represented by higher levels of high affinity IL-2R expression. Under the condition in which the cloned cells are exposed to a decreasing concentration of IL-2, SA1.4 and SA1.23 are found to secrete a greater amount of IFN-gamma. The present results therefore suggest that a control mechanism involving the "mutual amplification" of IL-2 and IFN-gamma regulates the differential expression of high affinity IL-2R on antigen-specific T4 clones.

An antigen-independent physiological activation pathway for L3T4+ T lymphocytes

The data presented in this report describe an antigen-independent activation pathway leading to reinduction of proliferation of class II major histocompatibility complex (MHC)-restricted murine T cell lines that after previous antigen-specific stimulation reverted to a resting state. Antigen-independent proliferation and interleukin 2 (IL2)-receptor expression occur in the presence of splenic accessory cells, exogenous IL2 and a soluble factor(s) provisionally termed T cell-stimulating factor(s) (TSF). Each of these components is essential for inducing growth. TSF is found in the supernatant of an autoreactive T cell line upon stimulation with syngeneic accessory cells. Neither TSF nor accessory cells can be replaced by IL1 and by some other cytokines. Monoclonal antibodies against class II MHC molecules, the T cell receptor and L3T4 do not block this antigen-independent stimulation. This demonstrates that the function of the accessory cell in this system is not MHC restricted and that the T cell receptor is also not involved. Furthermore, it is suggested that the blocking of L3T4 molecules by antibody will mediate a negative signal only if T cells are triggered via their antigen receptors.