When are patients with osteoarthritis referred for surgery?

Current treatment strategies in hip and knee osteoarthritis (OA) involve a combined approach that includes not only modification of risk factors and conservative treatment but also joint-preserving surgical therapy in the early stages, or joint replacement in late OA. With the recent development of new etiological concepts (i.e. hip dysplasia and femoroacetabular impingement as major risk factors for hip OA), treatment alternatives for joint preservation could be extended significantly. Satisfactory results of osteotomies and other reconstructive procedures around hip and knee joints can only be expected in early OA (Kellgren/Lawrence grade 0-II). If patients with advanced radiographic OA grades III-IV do not respond to conservative treatment over at least 3 months and express a relevant burden of disease, joint replacement might be considered. Prior to surgery, potential contraindications must be excluded, patient expectations need to be discussed, and modifiable risk factors, which may negatively influence the outcome, should be optimized.

Therapy-Induced Senescence: Opportunities to Improve Anticancer Therapy

Cellular senescence is an essential tumor suppressive mechanism that prevents the propagation of oncogenically activated, genetically unstable, and/or damaged cells. Induction of tumor cell senescence is also one of the underlying mechanisms by which cancer therapies exert antitumor activity. However, an increasing body of evidence from preclinical studies demonstrates that radiation and chemotherapy cause accumulation of senescent cells (SnCs) both in tumor and normal tissue. SnCs in tumors can, paradoxically, promote tumor relapse, metastasis, and resistance to therapy, in part, through expression of the senescence-associated secretory phenotype. In addition, SnCs in normal tissue can contribute to certain radiation- and chemotherapy-induced side effects. Because of its multiple roles, cellular senescence could serve as an important target in the fight against cancer. This commentary provides a summary of the discussion at the National Cancer Institute Workshop on Radiation, Senescence, and Cancer (August 10-11, 2020, National Cancer Institute, Bethesda, MD) regarding the current status of senescence research, heterogeneity of therapy-induced senescence, current status of senotherapeutics and molecular biomarkers, a concept of "one-two punch" cancer therapy (consisting of therapeutics to induce tumor cell senescence followed by selective clearance of SnCs), and its integration with personalized adaptive tumor therapy. It also identifies key knowledge gaps and outlines future directions in this emerging field to improve treatment outcomes for cancer patients.

Association of Premature Immune Aging and Cytomegalovirus After Solid Organ Transplant

Immune function is altered with increasing age. Infection with cytomegalovirus (CMV) accelerates age-related immunological changes resulting in expanded oligoclonal memory CD8 T cell populations with impaired proliferation, signaling, and cytokine production. As a consequence, elderly CMV seropositive (CMV⁺) individuals have increased mortality and impaired responses to other infections in comparison to seronegative (CMV^–) individuals of the same age. CMV is also a significant complication after organ transplantation, and recent studies have shown that CMV-associated expansion of memory T cells is accelerated after transplantation. Thus, we investigated whether immune aging is accelerated post-transplant, using a combination of telomere length, flow cytometry phenotyping, and single cell RNA sequencing. Telomere length decreased slightly in the first year after transplantation in a subset of both CMV⁺ and CMV^– recipients with a strong concordance between CD57⁺ cells and short telomeres. Phenotypically aged cells increased post-transplant specifically in CMV⁺ recipients, and clonally expanded T cells were enriched for terminally differentiated cells post-transplant. Overall, these findings demonstrate a pattern of accelerated aging of the CD8 T cell compartment in CMV⁺ transplant recipients.

THU0310 CASE–CONTROL SEROPREVALENCE STUDY ON THE ASSOCIATION BETWEEN BARTONELLA INFECTION AND ANTI-NEUTROPHIL CYTOPLASMIC ANTIBODY-ASSOCIATED VASCULITIS

Background:

Bartonellosis is an emerging anthropozoonosis caused by infection with intracellular Gram-negativeBartonellaspecies. It leads to necrotizing granulomas and endothelial damage and causes acute and chronic human diseases, such as cat scratch disease, bacillary angiomatosis and endocarditis. Endocarditis due toBartonella henselaeandB. quintanais reported to produce anti-neutrophil cytoplasmic antibodies (ANCAs) that disappear with effective antimicrobial treatment.

Objectives:

Hypothesizing a role forBartonellainfection in ANCA-associated vasculitis (AAV), which also includes granulomatous and vascular inflammation, we studied the seroprevalence of 5Bartonellaspecies in patients with AAV.

Methods:

The study used plasma samples from patients with granulomatosis with polyangiitis and microscopic polyangiitis that were enrolled in the Rituximab for AAV (RAVE) trial and from healthy controls living in the United States. Western blot assays were used for serological testing of infection withB. quintana,B. henselaeHouston-1,B. elizabethae,B. vinsoniisubsp.berkhoffiiandB. alsatica. The associations of positive serology results and AAV were expressed as odds ratios (OR). Clinical characteristics of seropositive and seronegative patients, assessed by the BVAS/WG instrument, were compared. These comparisons were done for 9 organ systems; in case they showed differences withP<0.10, the corresponding organ system-specific clinical features were also analyzed. Statistical analysis was performed using Fisher’s exact test or Student’s t-test, as appropriate.

Results:

We analyzed blood samples of 187 patients with AAV (collected at start of the trial) and of 127 controls. There were no significant differences between the cases and controls for mean age (P=0.148) and proportion of males (P=0.36).Bartonellaspp. serological testing was positive for 112 (60%) cases and 40 (31%) controls (OR 3.25 [95% CI 2.02–5.22],P<0.001). Significant associations were also found within subsets of PR3-AAV (OR 4.00 [95% CI 2.37–6.76],P<0.001), MPO-AAV (OR 2.18 [95% CI 1.17–4.06],P=0.017), newly-diagnosed (OR 3.89 [95% CI 2.21–6.86],P<0.001) and relapsing disease (OR 2.86 [95% CI 1.65–4.98],P<0.001). Species-specific positive serological testing was found in particular againstB. henselae(cases: 27%, controls: 0.8%; OR 39.93 [95% CI 5.42–293.90];P<0.001). Compared to AAV patients without seropositivity forBartonellaspp., AAV patients testing seropositive forBartonellaspp. had significantly more bloody nasal discharge (P=0.046), sinus involvement (P=0.035) and conjunctivitis/episcleritis (P=0.016).

Conclusion:

This study reveals higher seroprevalence ofBartonella, especiallyB. henselae, in patients with AAV than in healthy controls. Although cross-reactivity ofBartonellawith other microorganisms cannot be excluded, these results may support an etiopathogenic role ofBartonellainfection in AAV that deserves further investigation.

Disclosure of Interests:

Alfred Mahr Consultant of: Celgene, Speakers bureau: Roche, Chugai, Sophie Edouard: None declared, Divi Cornec: None declared, Solange GONZALEZ-CHIAPPE: None declared, Jörg Goronzy: None declared, Philippe Guilpain: None declared, Carol Langford: None declared, Pierre-Yves Lévy: None declared, Peter A. Merkel: None declared, Paul Monach: None declared, E. William St. Clair: None declared, Philip Seo: None declared, Robert Spiera Grant/research support from: Roche-Genetech, GSK, Boehringer Ingelheim, Chemocentryx, Corbus, Forbius, Sanofi, Inflarx, Consultant of: Roche-Genetech, GSK, CSL Behring, Sanofi, Janssen, Chemocentryx, Forbius, Mistubishi Tanabe, Cornelia Weyand: None declared, John H. Stone Grant/research support from: Roche, Consultant of: Roche, Didier Rauolt: None declared, Ulrich Specks: None declared

[Complication profile and revision concepts for megaprosthetic reconstruction following tumour resection at the hip]

BACKGROUND

Tumourous destruction of the periacetabular region and the proximal femur is a typical consequence of either primary malignant bone tumour manifestation or skeletal metastatic diseases. Pathological fractures of the proximal femur and periacetabular regions due to primary manifestation or metastatic disorders are frequent.

OBJECTIVES

Presentation of the most common complications of tumour endoprostheses at the hip and a description of management strategies, including therapeutic recommendations and concepts for complication avoidance.

MATERIALS AND METHODS

The current knowledge and our own experience of complication management with the use of megaprostheses around the hip are presented.

RESULTS

Compared to elective/primary total hip arthroplasty, megaprosthetic reconstructions following tumour resections have an increased rate of postoperative deep infections, dislocations, incidence of pathological and periprosthetic fractures and of deep vein thrombosis. The postoperative mortality and local tumour recurrence along with deep infections represent the most serious complications.

CONCLUSIONS

In comparison to primary arthroplasty, the risk of failure and complications following tumour-endoprosthetic replacement is increased. Precise surgical planning and careful selection and preoperative preparation of suitable patients should be performed in close interdisciplinary cooperation with final decision-making on an interdisciplinary tumour board. Wide resection and advanced reconstruction, as well as complicated palliative stabilization due to malignant bone tumour growth around the hip joint should be performed in musculoskeletal tumour centres with profound expertise in osteosynthetic and endoprosthetic reconstruction and consecutive complication management of the pelvis and the proximal femur.

Biomechanical comparison of bi- and tricortical k-wire fixation in tension band wiring osteosynthesis

Background

Patients with a simple transversal fracture of the olecranon are often treated with a tension band wiring (TBW), because it is known as a biomechanically appropriate and cost-effective procedure. Nevertheless, the technique is in detail more challenging than thought, resulting in a considerable high rate of implant-related complications like k-wire loosening and soft tissue irritation. In the literature, a distinction is generally only made between transcortical (bi-) and intramedullary (mono-) fixation of the wires. There is the additional possibility to fix the proximal bent end of k-wire in the cortex of the bone and thus create a tricortical fixation. The present study investigates the effectiveness of bi- and tricortical k-wire fixation in a biomechanical approach.

Methods

TBW of the olecranon was performed at 10 cadaver ulnas from six donors in a usual manner and divided into two groups: In group 1, the k-wire was inserted by bicortical fixation (BC), and in group 2, a tricortical fixation (TC) was chosen. Failure behavior and maximum pullout strength were assessed and evaluated by using a Zwick machine. The statistical evaluation was descriptive and with a paired t test for the evaluation of significances between the two techniques.

Results

The average age of the used donors was 81.5 ± 11.5 (62–92) years. Three donors were female, and three were male. Ten k-wires were examined in BC group and 10 in the TC group. The mean bone density of the used proximal ulnas was on average 579 ± 186 (336–899) HU. The maximum pullout strength was 263 ± 106 (125–429) N in the BC group and increased significantly in the TC group to 325 ± 102 (144–466) N [p = .005].

Conclusion

This study confirms for the first time biomechanical superiority of tricortical k-wire fixation in the olecranon when using a TBW and may justify the clinical use of this method.

Prospective randomized controlled trial in the treatment of lateral epicondylitis with a new dynamic wrist orthosis

BACKGROUND

In the treatment of lateral epicondylitis (LE), the role of a new dynamic wrist orthosis is unclear.

PATIENTS AND METHODS

Patients suffering from a LE longer than 3 months were multicentrically and prospectively randomized into a physiotherapeutic group (PT group) and in a physiotherapy group plus wrist orthosis (PT + O group). Physiotherapy consisted of daily eccentric strengthening exercises under initial professional supervision. Inclusion criteria were a Placzek score greater than 4. Exclusion criteria were previous surgery, rheumatic arthritis, elbow instability, radicular symptoms, higher-grade extensor tendon rupture, or cervical osteoarthritis. The clinical evaluation was performed after 12 weeks and 12 months. The Patient-Rated Tennis Elbow Evaluation (PRTEE) scale, Placzek Score, the pain rating (VAS), range of motion and the Subjective Elbow Score were evaluated.

RESULTS

Of the initially 61 patients, 31 were followed up after 12 weeks and 22 after 12 months. Twenty-nine patients (43%) were male, the mean age was 46, and 44 patients (66%) had the right elbow involved. At 12 weeks, there was a pain reduction on the VAS in both groups (PT + O: 6.5-3.7 [p = .001]; PT: 4.7-4.1 [p = .468]), albeit it was only significant for the PT + O group. At 12 months, reduction was significant in both groups (PT + O: 1.1 [p = .000]; PT: 1.3 [p = .000]). The painless maximum hand strength in kg improved in both groups significant after 3 and 12 months. The Placzek score was reduced from 8.25 to 3.5 [p = .001] after 12 weeks for the PT + O group and from 8.1 to 3.8 [p = .000] in the PT group, as well as after 12 months in the PT + O group to 0 [p = .000] and in the PT group to 2.0 [p = .000]. The PRTEE improved in both groups after 12 weeks (PT + O: 52.8--31.3 [p = .002]; PT: 48.6-37.6 [p = .185]) and 12 months (PT + O: 16.15 [p = .000]; PT: 16.6 [p = .000]), although the reduction at 12 weeks was not significant for the PT group.

CONCLUSION

The elbow orthosis appears to accelerate the healing process with respect to the PRTEE and pain on the VAS (12 weeks follow-up), although there is an adjustment after 12 months in both groups and a significant improvement of symptoms is achieved in all endpoints.

Response to Comment on "Diversification of the antigen-specific T cell receptor repertoire after varicella zoster vaccination"

In our repertoire studies of varicella zoster virus-specific T cells, we used very stringent computational criteria to keep contamination with T cell receptor sequences from bystander-activated T cells to a minimum.

[Total hip arthroplasty in overweight osteoarthritis patients]

BACKGROUND

An increasing number of patients scheduled for total hip arthroplasty (THA) are obese and exhibit a different risk profile from that of patients of normal weight.

OBJECTIVES

To provide an overview of the impact of obesity on the outcome of primary THA.

MATERIALS AND METHODS

Literature review and discussion of own epidemiological data.

RESULTS

Obese patients can expect as much functional improvement as non-obese patients after THA. However, peri- and postoperative complication (e.g., periprosthetic infection and dislocation) rates are reported to be increased in obese THA patients.

CONCLUSIONS

The knowledge of obesity-associated risks is the prerequiste for successful THA in obese patients.

[Arthroplasty for osteoarthritis secondary to hip dysplasia: Problem-oriented treatment strategies]

BACKGROUND

Because of anatomical variations total hip arthroplasty (THA) can be demanding in patients with osteoarthritis secondary to hip dysplasia.

OBJECTIVES

Depending on the degree of bony deformation, hip dislocation and soft tissue alteration numerous treatment strategies are available. This review describes current approaches that address frequent deformities.

MATERIALS AND METHODS

Review of relevant clinical studies, meta-analyses, and presentation of our own approach.

RESULTS

Pre-operative planning (based on a thorough clinical and radiographic examination) is essential. Acetabular reconstruction close to the primary acetabulum should always be intended. Roof augmentation and/or cup medialization can support stable bony implant fixation. Subtrochanteric shortening osteotomy of the femur is a demanding but reliable technique that avoids nerve damage in cases where inappropriate lengthening would be necessary (i.e., high riding dislocation).

CONCLUSIONS

Although the post-operative complication rate is elevated after THA for dysplastic hips compared with primary osteoarthritis, the overall functional results and implant survival are comparable.

[Avoidance, diagnostics and therapy of nerve lesions after total hip arthroplasty]

Nerve palsy following total hip arthroplasty is a rare complication. Developmental dysplasia of the hip, previous fracture treatment and medical comorbidities are characteristic risk factors. By accurate preparation of the patient and a careful operative technique nerve palsy can be avoided in most cases. Nerve palsy following poor patient positioning during the perioperative period should be avoided by close cooperation with anesthesiologists.In cases of postoperative nerve palsy correct diagnostics should be carried out immediately. Further treatment options should be considered to minimize the damage. For patients with definite nerve palsy, devices such as a foot drop splint are often necessary and should be carried out as soon as possible.

Role of increased guanosine triphosphate cyclohydrolase-1 expression and tetrahydrobiopterin levels upon T cell activation

Tetrahydrobiopterin (BH(4)) is an essential co-factor for the nitric-oxide (NO) synthases, and in its absence these enzymes produce superoxide (O(2)(·-)) rather than NO. The rate-limiting enzyme for BH(4) production is guanosine triphosphate cyclohydrolase-1 (GTPCH-1). Because endogenously produced NO affects T cell function, we sought to determine whether antigen stimulation affected T cell GTPCH-1 expression and ultimately BH(4) levels. Resting T cells had minimal expression of inducible NOS (NOS2), endothelial NOS (NOS3), and GTPCH-1 protein and nearly undetectable levels of BH(4). Anti-CD3 stimulation of T cells robustly stimulated the coordinated expression of NOS2, NOS3, and GTPCH-1 and markedly increased both GTPCH-1 activity and T cell BH(4) levels. The newly expressed GTPCH-1 was phosphorylated on serine 72 and pharmacological inhibition of casein kinase II reduced GTPCH-1 phosphorylation and blunted the increase in T cell BH(4). Inhibition of GTPCH-1 with diaminohydroxypyrimidine (1 mmol/liter) prevented T cell BH(4) accumulation, reduced NO production, and increased T cell O(2)(·-) production, due to both NOS2 and NOS3 uncoupling. GTPCH-1 inhibition also promoted TH(2) polarization in memory CD4 cells. Ovalbumin immunization of mice transgenic for an ovalbumin receptor (OT-II mice) confirmed a marked increase in T cell BH(4) in vivo. These studies identify a previously unidentified consequence of T cell activation, promoting BH(4) levels, NO production, and modulating T cell cytokine production.

TCR tuning by homeostatic cytokines — implication for autoimmunity (101.16)

In animal models, lymphopenia and the associated function of homeostatic cytokines (HC) set the stage for autoimmunity. This model is relevant for rheumatoid arthritis (RA) which has defects in T cell homeostasis due to a failure in DNA repair and which responds to JAK inhibition. We have previously shown that RA T cells have a hyperreactive ERK response which impairs the induction of anergy. Here, we examined whether HC tune TCR activation thresholds by calibrating the ERK rheostat. RA T cells exhibited increased levels of phosphorylated STAT3 and STAT5 indicating in vivo activity of IL-21/IL6 and IL-7/IL-15. Incubation of healthy donor T cells with IL-7, IL15 or IL21 prior to anti-CD3/CD28 stimulation augmented ERK activation and expression of activation markers (CD69, CD40L) and cytokines (TNFα, IFNγ and IL-17). Preincubation with IL-1β or TNFα did not exert an effect. In DR4 healthy donors, HC priming facilitated responses to self-antigens such as citrullinated vimentin peptide. The effect of HC lasted for less than 3 hours and was sensitive to PI3K inhibition suggesting a non-transcriptional PI3K mediated priming of the ERK pathway. HC dose titration showed a bimodal distribution in pERK consistent with an on-off switch characteristic of a positive feedback loop. Allosteric binding of RAS-GTP to SOS is known to induce such an on-off switch. Indeed, HC incubation increased active RAS. We propose that HC lower the threshold for autoimmune responses by priming of SOS.

Loss of miR-181a-mediated DUSP6 repression increases the TCR threshold of naive CD4 T cells in the elderly (85.11)

With increasing age, the ability of the immune system to respond to vaccination with a CD4 T cell response and the production of antibodies declines. The decline is only partially explained by a loss of naïve and central memory CD4 T cells due to thymic involution. Naïve CD4 T cells are present in sufficient, albeit compared to young adults reduced frequencies in most elderly suggesting that additional functional defects are important. In these studies, we compared naïve CD45RO- CD4+ T cells from 20 to 35 (n=117) and 70 to 85 (n=80) year-old healthy adults. Elderly T cells were less responsive to superantigen/dendritic cell (p&lt;0.001) stimulation. Signaling studies by PhosFlow showed reduced ERK (p&lt;0.0001), but normal ZAP70 phosphorylation in the first 5 minutes after stimulation, suggesting a selective age-related defect in the ERK pathway. In murine systems, DUSP6 has been implicated in differentiation-dependent TCR threshold calibration. In Western blot studies, DUSP6 protein was increased in elderly CD4 T cells (p=0.02), however, DUSP6 transcription was not different suggesting a defect in posttranscriptional regulation. Expression of miR-181a that binds to the DUSP6 3′UTR was decreased in elderly naïve CD4 T cells. Overexpression of miR-181a downregulated DUSP6 expression and restored ERK responses in elderly CD4 T cells. Our data suggest that loss of miR181a in naïve CD4 T cells increases the TCR threshold and contributes the immune defect in the elderly.

CD28(-) T cells: their role in the age-associated decline of immune function

The accumulation of CD28(-) T cells, particularly within the CD8 subset, is one of the most prominent changes during T-cell homeostasis and function associated with aging in humans. CD28, a major co-stimulatory receptor, is responsible for the optimal antigen-mediated T-cell activation, proliferation and survival of T cells. CD28(-) T cells exhibit reduced antigen receptor diversity, defective antigen-induced proliferation and a shorter replicative lifespan while showing enhanced cytotoxicity and regulatory functions. Gene expression analyses reveal profound changes of CD28(-) T cells in comparison to their CD28(+) counterparts and corroborate their functional differences. Here we review recent advances in our understanding of CD28(-) T cells and their role in the age-associated decline of immune function.

Role of the T cell in the genesis of angiotensin II induced hypertension and vascular dysfunction

Hypertension promotes atherosclerosis and is a major source of morbidity and mortality. We show that mice lacking T and B cells (RAG-1^−/− mice) have blunted hypertension and do not develop abnormalities of vascular function during angiotensin II infusion or desoxycorticosterone acetate (DOCA)–salt. Adoptive transfer of T, but not B, cells restored these abnormalities. Angiotensin II is known to stimulate reactive oxygen species production via the nicotinamide adenosine dinucleotide phosphate (NADPH) oxidase in several cells, including some immune cells. Accordingly, adoptive transfer of T cells lacking the angiotensin type I receptor or a functional NADPH oxidase resulted in blunted angiotensin II–dependent hypertension and decreased aortic superoxide production. Angiotensin II increased T cell markers of activation and tissue homing in wild-type, but not NADPH oxidase–deficient, mice. Angiotensin II markedly increased T cells in the perivascular adipose tissue (periadventitial fat) and, to a lesser extent the adventitia. These cells expressed high levels of CC chemokine receptor 5 and were commonly double negative (CD3⁺CD4⁻CD8⁻). This infiltration was associated with an increase in intercellular adhesion molecule-1 and RANTES in the aorta. Hypertension also increased T lymphocyte production of tumor necrosis factor (TNF) α, and treatment with the TNFα antagonist etanercept prevented the hypertension and increase in vascular superoxide caused by angiotensin II. These studies identify a previously undefined role for T cells in the genesis of hypertension and support a role of inflammation in the basis of this prevalent disease. T cells might represent a novel therapeutic target for the treatment of high blood pressure.

Selective induction of rheumatoid factors by superantigens and human helper T cells

Production of autoantibodies specific for the Fc region of autologous IgG, called rheumatoid factors (RF), is a characteristic finding in patients with rheumatoid arthritis (RA). To study the requirements regulating the synthesis of these autoantibodies, we have cloned human helper T cells and co-cultured them with purified B cells. To mimic cognate T-B cell interaction, we have used bacterial superantigens that function by cross-linking HLA molecules on the B cell with selected T cell receptor (TCR) molecules expressing a particular polymorphism of the V beta gene segment. Data presented here demonstrate that the staphylococcal enterotoxin D (SE D), but not other bacterial superantigens, exhibits an ability to induce IgM, IgG, and especially RF production, in B cells from RA patients and normal individuals. Comparison with the polyclonal antibody production in B cell cultures driven by anti-CD3-stimulated T cell clones confirmed that SE D shifted the repertoire of secreted antibodies toward immunoglobulins with Fc binding specificity, suggesting that SE D preferentially stimulates RF+ B lymphocytes. B cells with the potential to secrete RF were highly frequent in RA patients, requiring as few as 150 peripheral B cells/culture to detect RF in the culture supernatants. SE D-induced RF synthesis was strictly dependent on the presence of selected CD4+T helper cells and required a direct membrane contact between B cells and T helper cells. Here, we propose a model that SE D selectively induces RF production depending on the availability of SE D responsive T cells in the TCR repertoire of the responder.

[Nodular panniculitis: a manifestation of Lyme borreliosis?]

Infection with Borrelia burgdorferi can induce various skin manifestations. The type of skin manifestation and the histopathological picture depend on the stage of infection and vary from local inflammatory infiltrates to chronic atrophic skin disease. Involvement of subcutaneous tissue has been observed only very rarely. We report on two patients suffering from nodular panniculitis (Pfeifer-Weber-Christian) and present evidence that the disease was caused by Borrelia burgdorferi. In one of the cases Borrelia burgdorferi was repeatedly isolated from skin and subcutaneous tissue biopsies in spite of repeated high-dose therapy with ceftriaxone, Doxycycline and cefotaxime.

Immunosuppression by anti-CD4 treatment in vivo. Persistence of secondary antiviral immune responses

Elimination of CD4+ helper T cells by treatment with monoclonal antibodies (mcAb) in vivo has been used as a new mode of immunosuppression in organ transplantation and autoimmune diseases. To explore the potential risks of this therapeutic approach we have studied antiviral responses in mice depleted of CD4+ T cells. Depletion of CD4+ T cells in vivo completely suppressed the generation of a primary virus-specific cytotoxic response. Injection of high doses of recombinant interleukin-2 (rIL-2) given after virus immunization restored the responsiveness of helper cell-depleted mice to virus-expressing target cells, suggesting a crucial role of IL-2 in antiviral defense mechanisms. In contrast to primary responses, memory cytolytic responses to viral antigens persisted despite depletion of greater than 90% of CD4+ helper T cells. The generation of such memory cytotoxic responses was dependent upon help provided by CD4+ lymphocytes surviving the antibody therapy. After antibody treatment, frequencies of virus-specific helper cells were minimal in primed mice, excluding insufficient helper cell elimination as the reason for the persistence of memory responses. Data presented here suggest that there exist distinct helper pathways in primary and secondary cytolytic antiviral responses that might represent several subsets of helper T cells as well as differences in helper signals required by distinct effector cells.

Immunosuppression by anti-CD4 treatment in vivo. Cellular and humoral responses to alloantigens

Antibody-mediated elimination of CD4+ lymphocytes in vivo has been successfully used to suppress the humoral response to foreign antigens and to induce long-term tolerance. However, secondary humoral responses, as well as secondary cytolytic responses specific for viral antigens, could not be prevented, providing evidence for functional heterogeneity within the helper cell compartment. Data presented here support the notion that helper cell requirements for cellular responses to alloantigens are unique and do not involve CD4+ T lymphocytes. While the administration of anti-CD4 mcAb failed to suppress allospecific CTL responses, the formation of alloantibodies was initially inhibited in parallel to the deficiency in CD4+ helper cells. After regeneration of CD4+ T cells, the animals regained the ability to produce specific IgG alloantibodies. The dichotomy of helper pathways in humoral and cellular alloreactive responses challenges the concept of a single CD4+ helper cell population. Insights into the functional heterogeneity of helper cells for primary, secondary, and allospecific responses might open new avenues for selective manipulation of helper subpopulations.

Enhanced cell-mediated protection against fatal Escherichia coli septicemia induced by treatment with recombinant IL-2

Administration of rIL-2 to BALB/c mice induces a rapid, cell-mediated response that is sufficient to protect mice from a lethal i.p. dose of Escherichia coli. Mice were protected from septic death if IL-2 was administered i.p. within 1 h after the bacterial challenge. Optimal protection was provided by treating the lethally challenged mice with rIL-2 at 1 and 5 h or 1, 5, and 10 h after the bacterial challenge and was dose-dependent (greater than or equal to 5.0 x 10(5) U/kg). Furthermore, treatment of mice with anti-IL-2R antibody abolished the protective effect induced by rIL-2 administration. These data suggest that the rIL-2-induced protection against septic death in mice is mediated by a cell type expressing a functional IL-2R. One potentially important therapeutic application of rIL-2 may be to modulate the course of sepsis once the host has been exposed to potentially lethal microbial pathogens.

Enhanced cell-mediated protection against fatal Escherichia coli septicemia induced by treatment with recombinant IL-2

Administration of rIL-2 to BALB/c mice induces a rapid, cell-mediated response that is sufficient to protect mice from a lethal i.p. dose of Escherichia coli. Mice were protected from septic death if IL-2 was administered i.p. within 1 h after the bacterial challenge. Optimal protection was provided by treating the lethally challenged mice with rIL-2 at 1 and 5 h or 1, 5, and 10 h after the bacterial challenge and was dose-dependent (greater than or equal to 5.0 x 10(5) U/kg). Furthermore, treatment of mice with anti-IL-2R antibody abolished the protective effect induced by rIL-2 administration. These data suggest that the rIL-2-induced protection against septic death in mice is mediated by a cell type expressing a functional IL-2R. One potentially important therapeutic application of rIL-2 may be to modulate the course of sepsis once the host has been exposed to potentially lethal microbial pathogens.

Triggering of T-lymphocytes via either T3-Ti or T11 surface structures opens a voltage-insensitive plasma membrane calcium-permeable channel: requirement for interleukin-2 gene function

Stimulation of human T-lymphocytes via either the surface T3-Ti antigen-major histocompatibility complex receptor complex or the T11 molecule results in clonal proliferation through a calcium-dependent mechanism. To investigate this signal transduction, plasma membrane calcium-permeable channels were characterized in T-lymphocytes by means of whole cell or single channel patch-clamp recordings. Stimulation of T-lymphocytes via either structure results in opening of an identical set of voltage-insensitive plasma membrane Ca2+-permeable channels through the action of a diffusible second messenger. Previous work with excised inside-out patches suggests that inositol 1,4,5-trisphosphate is the activating second messenger of the voltage-insensitive T-cell Ca2+-permeable channel. Since there is a significant increase in phosphoinositide turnover after stimulation via either the T3-Ti or T11 pathway, it is suggested that triggering of either structure opens a common set of channels through this mechanism. Furthermore, currents flowing through Ca2+-permeable channels are apparently autoregulated, as inward conductance is abolished by elevation of Ca2+ concentration in the bathing solution. In particular, the steady-state rise in interleukin-2 (T-cell growth factor) mRNA is dependent on the rise of [Ca2+]i resulting from ion movement across this channel.

Administration in vivo of recombinant interleukin 2 protects mice against septic death

Administration in vivo of recombinant interleukin 2 (rIL-2) to mice induces a polyclonal IgM response. When co-administered with a specific antigen, rIL-2 can enhance concentrations of murine IgM antibodies specific for the antigen by fivefold within 7 d of initial treatment. IgM antibodies that are induced after injection of rIL-2 include antibodies specific for J5, a cell wall core lipopolysaccharide (LPS) antigen that is shared by the different members of the Enterobactericeae family. We report here that mice pretreated with rIL-2 or immunized with J5 antigen 7 d before bacterial challenge were protected from septic death that is caused by intraperitoneal challenges with Escherichia coli. Optimal protection was provided by a combined J5 antigen and rIL-2 treatment. Acquisition of the rIL-2 and J5 antigen-induced protection against lethal bacterial infection coincided temporally with maximal serum IgM titers that also contained IgM antibodies specific for the J5 antigen. In passive immunization experiments, the affinity-purified IgM fraction in sera of rIL-2-treated animals was identified as necessary and sufficient for protection. The IgM-depleted serum had no protective effect. The nonspecific augmentation of host-defense mechanisms without the induction of endotoxin manifestations makes rIL-2 a potential candidate to any alternative LPS-containing vaccines for the prevention of bacterial infections by gram-negative organisms since the core LPS antigen is shared among gram-negative bacteria.

Heterogeneity of signal requirements in T cell activation within a panel of human proliferative T cell clones

Activation of T lymphocytes is initiated by receptor ligand interactions at the cell surface leading to the transduction of intracellular signals followed by the de novo synthesis and expression of T cell activation markers (including receptors for interleukin 2 (IL 2) and transferrin), production of lymphokines, and T cell proliferation. This requisite first step for activation of T lymphocytes can be mimicked in certain situations with a variety of stimuli. These include antibodies to certain integral membrane proteins, phorbol esters, and plant lectins that act as mitogens. In this paper, we report that at least two classes of human T cell clones can be distinguished based upon signal requirements necessary to induce proliferation. Although all clones analyzed expressed IL 2 receptors and secreted IL 2 after non-antigenic activation, one subset of clones did not proliferate in response to the same non-antigenic signals. In that subset, complete activation leading to proliferation required interaction of the T cell with specific antigen. The ability to subset these T cell clones into two groups did not correlate with phenotypic differences, source of the clone, nor with magnitude of intracellular calcium mobilization. By studying the stimulation requirements of these two subsets of human T cell clones through the use of specific antigen or antigen-independent stimuli, it was possible to demonstrate that different stimuli varied in their ability to induce steps of T cell activation. Analysis of reactivity of these clones to suboptimal stimulation allowed the definition of intermediate stages of T cell activation. Such intermediate stages might reflect a diversity of intracellular signaling pathways or a complexity of regulatory mechanisms distal to the events that allow intracellular calcium mobilization. Thus for the first time, it has been possible to study ordered events of T cell activation in non-transformed, antigen-dependent human T lymphocytes. The data presented in this paper suggest that T cell activation is not an all or nothing phenomenon, and there is an ordered sequence of events that can be differentiated based upon signal requirements at the T cell membrane.

Heterogeneity of signal requirements in T cell activation within a panel of human proliferative T cell clones

Activation of T lymphocytes is initiated by receptor ligand interactions at the cell surface leading to the transduction of intracellular signals followed by the de novo synthesis and expression of T cell activation markers (including receptors for interleukin 2 (IL 2) and transferrin), production of lymphokines, and T cell proliferation. This requisite first step for activation of T lymphocytes can be mimicked in certain situations with a variety of stimuli. These include antibodies to certain integral membrane proteins, phorbol esters, and plant lectins that act as mitogens. In this paper, we report that at least two classes of human T cell clones can be distinguished based upon signal requirements necessary to induce proliferation. Although all clones analyzed expressed IL 2 receptors and secreted IL 2 after non-antigenic activation, one subset of clones did not proliferate in response to the same non-antigenic signals. In that subset, complete activation leading to proliferation required interaction of the T cell with specific antigen. The ability to subset these T cell clones into two groups did not correlate with phenotypic differences, source of the clone, nor with magnitude of intracellular calcium mobilization. By studying the stimulation requirements of these two subsets of human T cell clones through the use of specific antigen or antigen-independent stimuli, it was possible to demonstrate that different stimuli varied in their ability to induce steps of T cell activation. Analysis of reactivity of these clones to suboptimal stimulation allowed the definition of intermediate stages of T cell activation. Such intermediate stages might reflect a diversity of intracellular signaling pathways or a complexity of regulatory mechanisms distal to the events that allow intracellular calcium mobilization. Thus for the first time, it has been possible to study ordered events of T cell activation in non-transformed, antigen-dependent human T lymphocytes. The data presented in this paper suggest that T cell activation is not an all or nothing phenomenon, and there is an ordered sequence of events that can be differentiated based upon signal requirements at the T cell membrane.

Modulation of CD4 by antigenic activation

Cell surface expression of CD4, an invariant membrane glycoprotein, is characteristic of the MHC class II-restricted T cell helper/inducer subset. Although the specificity and restriction patterns of T lymphocytes are determined by the T cell receptor for antigen, CD4 might represent an additional "interaction" molecule that is required to strengthen the interaction between T cells, antigen, and antigen-presenting cells. In this manuscript, we have shown that the cell surface expression of CD4 is correlated with activation of T cells. Data presented in this paper have demonstrated, for the first time, that antigenic stimulation of human T cell clones caused a decrease in the expression of the CD4 marker (as well as to the CD3 marker) to about 50% of the constitutive level. As previously demonstrated, PMA caused modulation of CD4 and CD3, which suggested that phosphorylation by protein kinase C played a crucial role in the regulation of the expression of both markers. The parallel down-regulation of CD3 and CD4 after antigen stimulation suggested that both markers might be members of a multimolecular complex mediating T cell activation.

Modulation of CD4 by antigenic activation

Cell surface expression of CD4, an invariant membrane glycoprotein, is characteristic of the MHC class II-restricted T cell helper/inducer subset. Although the specificity and restriction patterns of T lymphocytes are determined by the T cell receptor for antigen, CD4 might represent an additional "interaction" molecule that is required to strengthen the interaction between T cells, antigen, and antigen-presenting cells. In this manuscript, we have shown that the cell surface expression of CD4 is correlated with activation of T cells. Data presented in this paper have demonstrated, for the first time, that antigenic stimulation of human T cell clones caused a decrease in the expression of the CD4 marker (as well as to the CD3 marker) to about 50% of the constitutive level. As previously demonstrated, PMA caused modulation of CD4 and CD3, which suggested that phosphorylation by protein kinase C played a crucial role in the regulation of the expression of both markers. The parallel down-regulation of CD3 and CD4 after antigen stimulation suggested that both markers might be members of a multimolecular complex mediating T cell activation.

Single-channel and whole-cell recordings of mitogen-regulated inward currents in human cloned helper T lymphocytes

Cytoplasmic free Ca2+ [( Ca2+]i) appears to be an important signal for DNA synthesis in early stages of lymphocyte activation. In spite of many experimental studies which employ fluorescent Ca2+ indicator dye to demonstrate an early increase of [Ca2+]i in T-lymphocytes after stimulation with lectins, specific antigens, and monoclonal antibodies to T-lymphocyte receptors, the mechanism responsible for the rise of [Ca2+]i is unknown. We have used the extracellular patch clamp technique to investigate this mechanism. Unitary inward currents, mediated by Ca2+ or Ba2+, were recorded in the membrane of T-lymphocytes. The inward current channel was characterized by a conductance of 7 pS and extrapolated reversal potential (Erev) 110 mV positive to resting potential (Vr). While gating kinetic parameters were not affected by membrane potential changes, the probability of channel opening markedly increased upon activation of the T-lymphocyte by the mitogenic lectin, phytohaemagglutinin (PHA). PHA also evoked a cadmium-sensitive, inward Ba2+ current on whole-cell clamp. We suggest that this mitogen-regulated channel introduces Ca2+ into the cytoplasm upon activation and represents a new class of voltage-independent Ca2+ channels.

Long-term humoral unresponsiveness in vivo, induced by treatment with monoclonal antibody against L3T4

mAbs directed against the L3T4 molecule administered in vivo caused a severe and long lasting helper cell depletion in mice. Regeneration of the L3T4+ subpopulation occurred gradually (2-3 mo) after a single antibody treatment. Experiments were designed to examine the humoral immunocompetence of such anti-L3T4-treated animals during and after regeneration of the L3T4+ T cell subset. The animals were injected with anti-L3T4, immunized with soluble antigen, and challenged with antigen every 2 wk. Antibody responses to two antigens, sperm whale myoglobin (SpWMb) and KLH, which differ with regard to their immunogenicity, were compared. The lack of humoral immune responsiveness to either of these two antigens shorty after anti-L3T4 treatment responsiveness to either of these two antigens shortly after anti-L3T4 treatment was probably due to clonal depletion. The anti-L3T4-induced immunosuppressive effect on antibody production seemed to be determined in part by the preexisting T cell repertoire, as was suggested by the recovery of responsiveness to the highly immunogenic antigen KLH and the transient inhibitory effect of anti-L3T4 treatment in primed animals. The regenerating L3T4+ T cell subpopulation was relatively incompetent in initiating B cell responses. More than 40% of the L3T4+ T cell compartment had to recover to provide help for the production of anti-KLH antibodies, whereas elimination of 90% of the L3T4+ helper cells did not inhibit a primary anti-KLH response. Evidence for a heterogeneous composition of the L3T4+ subset came from experiments using rIL-2 in vivo. The addition of rIL-2 during early helper cell depletion improved the recovery of the humoral responsiveness without apparently affecting the kinetics of the regeneration of L3T4+ T cells. Interestingly, humoral unresponsiveness to the weakly immunogenic antigen SpWMb persisted for at least 120 d. This long lasting unresponsiveness could not be explained by clonal depletion, and suggested as one possibility that the presence of antigen during regeneration of the L3T4+ helper cell population may have influenced the ultimate T cell repertoire.

Gene conversion. A mechanism to explain HLA-D region and disease association

In speculating about mechanisms that might give rise to T-cell epitopes appearing within different HLA-DR frameworks, we return to the hypothesis expressed above that suggests that gene-conversion-like events might be involved in shuffling the hypervariable segments of HLA-D region exons into alternative HLA-D region frameworks where they will still be recognized by the T cell (but not typed by conventional serology or mixed lymphocyte typing) as the "disease associated" HLA product. This might well explain the lack of stringent association between rheumatoid arthritis and HLA-DR4. It is possible, through the use of such alloreactive T-cell clones, that we might eventually define subgroups based upon presumed genetic susceptibility markers, which might allow therapeutic or prognostic assignment of patients with seropositive rheumatoid arthritis.

Administration of recombinant interleukin 2 in vivo induces a polyclonal IgM response

We studied the potential immunoenhancing effects of high doses of rIL-2 on murine T and B cell functions in vivo. Injection of rIL-2 caused a threefold or more increase in the frequencies of antigen-specific proliferative T cells, suggesting that rIL-2 initiated a polyclonal T cell response. In primary and secondary humoral immune responses, administration of rIL-2 in vivo selectively enhanced the production of IgM antibodies, whereas the IgG response was unaffected. Coadministration of rIL-2 with antigen failed to induce an isotype switch from IgM to IgG in genetically low-responding mice. Interestingly, in mice treated with rIL-2 alone (in the absence of exogenous antigen), polyclonal IgM production was induced. Polyclonal IgM production of lesser magnitude was found when mice were immunized with specific antigen in the absence of exogenous rIL-2, suggesting that local IL-2 concentrations in a primary immune response might be sufficient to elicit a polyclonal IgM response.

Shared T cell recognition sites on human histocompatibility leukocyte antigen class II molecules of patients with seropositive rheumatoid arthritis

Seropositive rheumatoid arthritis (RA) in adult and juvenile patients is associated with the serologic marker HLA-DR4. This association is incomplete; about one-third of the patients lack the disease-associated HLA-DR4 haplotype. The main biological function of class II molecules is to restrict the recognition of antigen by T lymphocytes. We therefore tested the hypothesis that patients with seropositive RA share T cell recognition sites for an unknown antigen and that such T cell "epitopes" are not identified by conventional serologic typing. We generated alloreactive human T cell clones by stimulating peripheral blood lymphocytes of normal donors against a lymphoblastoid cell line from a juvenile patient with seropositive RA. A panel of clones that recognized only HLA-Dw14 cells on a panel of homozygous typing cells was used to analyze class II molecules of adult patients with seropositive RA. By inhibition studies using monoclonal antibodies, the epitopes recognized by the different clones could be further characterized and assigned either to DR- or to DQ-encoded cell surface products. By using four different clones, it was possible to identify Dw14-associated T cell epitopes on all seropositive rheumatoid patients tested who typed HLA-DR4-positive and also on all eight DR4-negative patients tested. Approximately one-half of nonrheumatoid DR4-positive donors carried one or more determinants recognized by these clones; the expression of these allodeterminants in DR4-negative nonrheumatoid patients was rare (less than 10%). Thus, alloreactive human T cell clones are powerful tools to define T cell recognition sites on class II molecules that are not identified by conventional typing. Using T cell clones with specificities for determinants expressed on Dw14 homozygous typing lines, we were able to demonstrate shared epitopes on cells of all patients tested with seropositive RA irrespective of their HLA-D or HLA-DR type. These data suggest that major histocompatibility complex class II antigens of RA patients might be much more homogeneous than demonstrated by the incomplete HLA-DR4 association.

T cell activation: differences in the signals required for IL 2 production by nonactivated and activated T cells

Soluble antibodies against the T3/antigen receptor complex alone are not sufficient to induce proliferation and interleukin 2 expression by T lymphocytes. An additional requirement is the presence of accessory cells (AC). In this model, AC provide at least two functions required for T cell activation: 1) the surface interaction of T3 antibodies with Fc receptors on the AC surface and 2) the production of soluble mediators such as interleukin 1 (IL 1). In the experiments reported here, these stimuli are represented by T3 antibodies immobilized onto Sepharose beads and by recombinant IL 1. In this study we investigated differences in activation requirements in resting and activated T cells. Resting T cells were represented by AC-depleted peripheral blood mononuclear cells (PBMC) or the T cell line Jurkat, which phenotypically resembles a resting T cell. Activated T cells were represented by T cell clones and the T cell line HUT 78, which express the activation molecules Ia and the IL 2 receptor (Tac). In resting cells, activation required the presence of three different signals: perturbation of the T3/antigen receptor complex by T3 antibodies, surface redistribution of T3/antigen receptor complexes, and presence of IL 1. In contrast, activated T cells require only perturbation and redistribution of T3/antigen receptor complexes and not IL 1 for the induction of proliferation or IL 2 production. Possible mechanisms of intracellular signaling for these stimuli are discussed.

T cell activation: differences in the signals required for IL 2 production by nonactivated and activated T cells

Soluble antibodies against the T3/antigen receptor complex alone are not sufficient to induce proliferation and interleukin 2 expression by T lymphocytes. An additional requirement is the presence of accessory cells (AC). In this model, AC provide at least two functions required for T cell activation: 1) the surface interaction of T3 antibodies with Fc receptors on the AC surface and 2) the production of soluble mediators such as interleukin 1 (IL 1). In the experiments reported here, these stimuli are represented by T3 antibodies immobilized onto Sepharose beads and by recombinant IL 1. In this study we investigated differences in activation requirements in resting and activated T cells. Resting T cells were represented by AC-depleted peripheral blood mononuclear cells (PBMC) or the T cell line Jurkat, which phenotypically resembles a resting T cell. Activated T cells were represented by T cell clones and the T cell line HUT 78, which express the activation molecules Ia and the IL 2 receptor (Tac). In resting cells, activation required the presence of three different signals: perturbation of the T3/antigen receptor complex by T3 antibodies, surface redistribution of T3/antigen receptor complexes, and presence of IL 1. In contrast, activated T cells require only perturbation and redistribution of T3/antigen receptor complexes and not IL 1 for the induction of proliferation or IL 2 production. Possible mechanisms of intracellular signaling for these stimuli are discussed.