Golfers are physically more active and have greater health associated quality of life than non-golfers following lower limb arthroplasty.

Background: The health benefits of physical activity are well recognised. This study assessed whether golfers were more physically active after lower limb arthroplasty when compared to those that did not play golf (primary outcome). In addition pre and postoperative changes in health-associated quality of life (HAQoL) and joint specific outcomes between golfers and none golfers were assessed (secondary outcomes). Methods: There were 304 patients [THA (n = 155) or TKA (n = 149)] prospectively registered during a 4-month period undergoing lower limb arthroplasty. The mean age was 70.0 (range 37-92, standard deviation 10.2) years and included 188 (61%) females and 120 (39%) males. They completed pre and postoperative questionnaires assessing recreational activity, physical activity, HAQoL (EuroQol [EQ]), joint specific health (Oxford scores), and satisfaction. Results: Golfers (n = 33, 10.9%) were more likely to achieve longer than 3 hours of moderate activity during a week (48.5% vs 38.0%, odds ratio (OR) 3.4, p = 0.045) and achieved their recommended activity level (96.8% vs 77.7%, OR 8.6, p = 0.015) compared to non-golfers following arthroplasty. Postoperative EQ5D (p = 0.034) and EQVAS (p = 0.019) were significantly greater in golfers. The joint specific Oxford hip score was greater in golfers compared to non-golfers (mean difference 5.6, p = 0.022), however no difference was observed in the Oxford knee score following TKA (p = 0.495). Conclusion: Golfers were more likely to achieve their weekly recommended level of physical activity and had a greater HAQoL relative to those that did not play golf following lower limb arthroplasty. More specifically after THA golfers also had a greater postoperative joint specific outcome, but no such advantage was observed in those following TKA. Evidence Level: Level II, diagnostic study.

A Cost-Utility Analysis of Robotic Arm-Assisted Total Hip Arthroplasty: Using Robotic Data from the Private Sector and Manual Data from the National Health Service.

Purpose: The aim was to assess the cost-effectiveness of robotic arm-assisted total hip arthroplasty (rTHA) compared with manual total hip arthroplasty (mTHA) and to assess the influence of annual volume on the relative cost-effectiveness of rTHA. Methods: A database of both rTHA (n = 48 performed in a private centre) and mTHA (n = 512 performed in the National Health Service) was used. Patient demographics, preoperative Oxford hip score, forgotten joint score, EuroQol 5-dimensional 3-level (EQ-5D), and postoperative EQ-5D were recorded. Two models for incremental cost-effectiveness ratios using cost per quality-adjusted life year (QALY) for rTHA were calculated based on a unit performing 100 rTHAs per year: 10-year follow-up and a lifetime time horizon (remaining life expectancy of a 69-year-old patient). Results: When adjusting for confounding factors, rTHA was independently associated with a 0.091 (p=0.029) greater improvement in the EQ-5D compared to mTHA. This resulted in a 10-year time horizon cost per QALY for rTHA of £1,910 relative to mTHA, which increased to £2,349 per QALY when discounted (5%/year). When using the 10-year time horizon cost per QALY was approximately £3,000 for a centre undertaking 50 rTHAs per year and decreased to £1,000 for centre undertaking 200 rTHAs per year. Using a lifetime horizon, the incremental unadjusted cost per QALY gained was £980 and £1432 when discounted (5%/year) for rTHA compared with mTHA. Conclusions: Despite the increased cost associated with rTHA, it was a cost-effective intervention relative to mTHA due to the associated greater health-related quality of health gain, according to the EQ-5D outcome measure.

Robotic-assisted unicompartmental knee arthroplasty has a greater early functional outcome when compared to manual total knee arthroplasty for isolated medial compartment arthritis.

AIMS: The primary aim of the study was to compare the knee-specific functional outcome of robotic unicompartmental knee arthroplasty (rUKA) with manual total knee arthroplasty (mTKA) for the management of isolated medial compartment osteoarthritis. Secondary aims were to compare length of hospital stay, general health improvement, and satisfaction between rUKA and mTKA. METHODS: A powered (1:3 ratio) cohort study was performed. A total of 30 patients undergoing rUKA were propensity score matched to 90 patients undergoing mTKA for isolated medial compartment arthritis. Patients were matched for age, sex, body mass index (BMI), and preoperative function. The Oxford Knee Score (OKS) and EuroQol five-dimension questionnaire (EQ-5D) were collected preoperatively and six months postoperatively. The Forgotten Joint Score (FJS) and patient satisfaction were collected six months postoperatively. Length of hospital stay was also recorded. RESULTS: There were no significant differences in the preoperative demographics (p ⩾ 0.150) or function (p ⩾ 0.230) between the groups. The six-month OKS was significantly greater in the rUKA group when compared with the mTKA group (difference 7.7, p < 0.001). There was also a greater six-month postoperative EQ-5D (difference 0.148, p = 0.002) and FJS (difference 24.2, p < 0.001) for the rUKA when compared to the mTKA. No patient was dissatisfied in the rUKA group and five (6%) were dissatisfied in the mTKA, but this was not significant (p = 0.210). Length of stay was significantly (p < 0.001) shorter in the rUKA group (median two days, interquartile range (IQR) 1 to 3) compared to the mTKA (median four days, IQR 3 to 5). CONCLUSION: Patients with isolated medial compartment arthritis had a greater knee-specific functional outcome and generic health with a shorter length of hospital stay after rUKA when compared to mTKA.Cite this article: Bone Joint Res 2019;9(1):15-22.

Early functional outcomes after condylar-stabilizing (deep-dish) versus standard bearing surface for cruciate-retaining total knee arthroplasty.

AIMS: The primary study aim was to compare early knee-specific function of patients undergoing cemented total knee arthroplasty (TKA) with either a cruciate-retaining (CR) polyethylene insert or a highly congruent condylar-stabilizing (CS) insert. Secondary aims were to compare general health and satisfaction between the groups. METHODS: A total of 418 consecutive primary TKAs were identified retrospectively. Demographics and preoperative and 1-year postoperative patient-reported outcome measures (PROMs) were collected prospectively. PROMs consisted of Oxford Knee Scores, EuroQol-5 Dimensions scores, and Short Form-12 scores. RESULTS: A total of 54 (12.9%) patients received a CS insert and 364 patients received a CR TKA. The CS group had a significantly (odds ratio (OR) 2.9; p = 0.002) greater proportion of females (77.8% versus 54.9%). The only significant difference in postoperative PROMs was a higher Short Form-12 physical component score in the CR group (difference 3.1; 95% confidence interval (CI) 0.1 to 6.1; p = 0.04). Linear regression analysis demonstrated no significant difference for all postoperative PROMs (p > 0.25). There was no significant difference in satisfaction rate (OR 0.94; 95% CI 0.42 to 2.12; p = 0.56) or pain visual analogue score (difference 6.1; 95% CI -1.9 to 14.0; p = 0.14) between the groups. CONCLUSION: More congruent CS inserts have equivalent PROMs and patient satisfaction at 1 year compared with less congruent CR inserts. These represent an option for surgeons undertaking TKA where increased congruency is desired.

Effects of Changing Meteoric Precipitation Patterns on Groundwater Temperature in Karst Environments.

Climate predictions indicate that precipitation patterns will change and average air temperatures will increase across much of the planet. These changes will alter surface water and groundwater temperatures which can significantly affect the local and regional environment. Here, we examine the role of precipitation timing in changes to groundwater temperature in carbonate-karst aquifers using measured groundwater level and temperature data from the Konza Prairie Long-Term Ecological Research Site, Kansas. We demonstrate that shifts to increased cool-season precipitation may mitigate the increases in groundwater temperature produced by increases in average annual air temperature. In karst, the solution-enlarged conduits allow faster and focused recharge, and the recharge-event temperature can strongly influence the groundwater temperature in the aquifer. Our field data and analysis show that predictions of future groundwater conditions in karst aquifers need to consider changes in precipitation patterns, in addition to changes to average annual air temperature.

A study of thromboprophylactic practices of Scottish orthopaedic surgeons in patients undergoing total hip replacements. Should practice change with new guidelines?

Despite increasing scientific investigation, the best method for preventing postoperative thromboembolism in patients undergoing a total hip replacement (THR) remains unclear. National Institute for Health and Clinical Excellence (NICE) and Scottish Intercollegiate Guidelines Network (SIGN) guidelines on the prevention of thromboembolism have caused much controversy. We surveyed Scottish surgeons regarding their thromboprophylaxis prescribing after THR. Questionnaires were sent to all Scottish orthopaedic consultants. They were asked about routine pharmacological and mechanical prophylaxis in patients undergoing a THR. Comparison was made with a previous survey done in 2003. The response rate was 75%. The survey showed an increased use of pharmacological prophylaxis from 93% to 100%. This was due to the increased use of aspirin from 51% to 64%. The use of low molecular weight heparin has remained constant at 51%. No surgeons routinely use warfarin, un-fractionated heparin or fondaparinux. Use of graded compression stockings has increased from 59% to 70%. In conclusion, there is increasing evidence that patients undergoing THR should receive extended prophylaxis for up to 35 days. Oral agents such as dabigatran and rivaroxaban have offered a new option for oral extended prescribing. The results in change of practice must be closely audited.

Constraints on the formation age of cometary material from the NASA Stardust mission.

We measured the 26Al-26Mg isotope systematics of a approximately 5-micrometer refractory particle, Coki, returned from comet 81P/Wild 2 in order to relate the time scales of formation of cometary inclusions to their meteoritic counterparts. The data show no evidence of radiogenic 26Mg and define an upper limit to the abundance of 26Al at the time of particle formation: 26Al/27Al < 1 x 10(-5). The absence of 26Al indicates that Coki formed >1.7 million years after the oldest solids in the solar system, calcium- and aluminum-rich inclusions (CAIs). The data suggest that high-temperature inner solar system material formed, was subsequently transferred to the Kuiper Belt, and was incorporated into comets several million years after CAI formation.

Hyporesponsiveness of intestinal dendritic cells to TLR stimulation is limited to TLR4.

Dendritic cells (DCs) are crucial to intestinal immune regulation because of their roles in inducing protective immunity against pathogens while maintaining tolerance to commensal bacteria. Nonetheless, relatively little is known about intestinal DC responsiveness to innate immune stimuli via TLRs. We have previously shown that DCs migrating from the rat intestine in lymph (iLDCs) are hyporesponsive to LPS stimulation, thus possibly preventing harmful immune responses being induced to commensal flora. In this study, to understand how iLDC function is regulated by innate immune stimuli, we have characterized the expression and function of TLRs in iLDCs isolated from the thoracic duct lymph of mesenteric lymphadenectomized rats and compared these with DCs grown from bone marrow in the presence of Flt3 ligand. We show that iLDCs express mRNAs for all TLRs, but express significantly less TLR4 mRNA than bone marrow-derived DCs. Functionally, iLDCs could be activated by TLR agonists representing intestinal pathogen-associated molecular patterns, with the important exception of the TLR4 agonist LPS. Furthermore, we show that DCs in the intestinal wall interact directly with noninvasive bacteria (Bacillus subtilis spores), leading to an increase in the output of activated iLDCs into lymph, and that DCs containing spores are activated selectively. These data highlight a functional difference between TLR4 and other TLRs. As iLDCs can respond to TLR stimulation in vitro, there must be other mechanisms that prevent their activation by commensal bacteria under steady-state conditions.

Steady-state migrating intestinal dendritic cells induce potent inflammatory responses in naive CD4+ T cells.

Steady-state dendritic cells (DCs) migrating in the lymph from the intestine induce tolerance to harmless intestinal antigens, preventing inflammatory responses. To determine if such DCs are inherently tolerogenic we collected intestinal lymph DCs (L-DCs) by cannulation of the thoracic duct of rats after mesenteric lymphadenectomy, and examined their capacity to activate naive CD4+ lymphocytes in an allogeneic mixed leucocyte reaction. L-DCs stimulated strong proliferative responses, induced secretion of inflammatory cytokines including interferon-gamma, and induced FoxP3-positive lymphocytes to divide. To determine if the activated CD4+ T cells had been tolerized, they were rested and restimulated with irradiated splenocytes. The restimulated CD4+ T cells again proliferated and secreted inflammatory cytokines. These data demonstrate that the DCs, which migrate from the intestine in the steady state, are paradoxically able to induce strong inflammatory responses from naive T cells, despite their role in the maintenance of oral tolerance.

New insights into the roles of dendritic cells in intestinal immunity and tolerance.

Dendritic cells (DCs) play a critical key role in the initiation of immune responses to pathogens. Paradoxically, they also prevent potentially damaging immune responses being directed against the multitude of harmless antigens, to which the body is exposed daily. These roles are particularly important in the intestine, where only a single layer of epithelial cells provides a barrier against billions of commensal microorganisms, pathogens, and food antigens, over a huge surface area. In the intestine, therefore, DCs are required to perform their dual roles very efficiently to protect the body from the dual threats of invading pathogens and unwanted inflammatory reactions. In this review, we first describe the biology of DCs and their interactions with other cells types, paying particular attention to intestinal DCs. We, then, examine the ways in which this biology may become misdirected, resulting in inflammatory bowel disease. Finally, we discuss how DCs potentiate immune responses against viral, bacterial, parasitic infections, and their importance in the pathogenesis of prion diseases. We, therefore, provide an overview of the complex cellular interactions that affect intestinal DCs and control the balance between immunity and tolerance.

Plasmacytoid dendritic cells do not migrate in intestinal or hepatic lymph.

Plasmacytoid dendritic cells (pDCs) recognize pathogen-associated molecules, particularly viral, and represent an important mechanism in innate defense. They may however, also have roles in steady-state tolerogenic responses at mucosal sites. pDCs can be isolated from blood, mucosa, and lymph nodes (LNs). Although pDCs can express peripherally derived Ags in LNs and at mucosal sites, it is not clear whether pDCs actually migrate from the periphery in lymph or whether LN pDCs acquire Ags by other mechanisms. To determine whether pDCs migrate in lymph, intestine or liver-draining LNs were removed and thoracic duct leukocytes (TDLs) were collected. TDLs expressing MHC-II and CD45R, but not TCRalphabeta or CD45RA, were then analyzed. These enriched TDLs neither transcribe type I IFNs nor secrete inflammatory cytokines in response to viral stimuli in vitro or after a TLR7/8 stimulus in vivo. In addition, these TDLs do not express CD5, CD90, CD200, or Siglec-H, but do express Ig, and therefore represent B cells, despite their lack of CD45RA expression. Intestinal and hepatic lymph are hence devoid of bona fide pDCs under both steady-state conditions and after TLR7/8 stimulation. This shows that any role for pDCs in Ag-specific T cell activation or tolerance must differ from the roles of classical dendritic cells, because it cannot result from peripheral Ag capture, followed by migration of pDCs via lymph to the LN.

A distinct subset of intestinal dendritic cells responds selectively to oral TLR7/8 stimulation.

The intestinal innate immune system continually interacts with commensal bacteria, thus oral vaccines should induce extra/alternative activation of DC, potentially through TLR. To examine this we collected intestinal lymph DC (iL-DC) under steady-state conditions and after feeding resiquimod (R-848), a synthetic TLR7/8 ligand, which we showed induces complete emptying of gut DC into lymph. iL-DC are heterogeneous with subset-specific functions. In this study we determined the kinetics of iL-DC subset release, activation and cytokine secretion induced by R-848. We show that L-DC comprise three distinct subsets (CD172ahigh, CD172aint and CD172alow) present with similar frequencies in intestinal but not hepatic lymph. No iL-DC express TLR7 mRNA, and only CD172a+ iL-DC express TLR8. However, after oral R-848 administration, output of all three subsets increases dramatically. CD172ahigh DC release precedes that of CD172alow DC, and the increased frequency of CD25high iL-DC is restricted to the two CD172a+ subsets. After feeding R-848 only CD172ahigh iL-DC secrete IL-6 and IL-12p40. However, CD172aint and CD172ahigh DC secrete similar but markedly lower amounts when stimulated in vitro. These results highlight the importance of in vivo approaches to assess adjuvant effects on DC and give novel insights into the subset-specific effects of an oral TLR ligand on intestinal DC.

Regulation of intestinal dendritic cell migration and activation by plasmacytoid dendritic cells, TNF-alpha and type 1 IFNs after feeding a TLR7/8 ligand.

Dendritic cells (DCs) migrating via lymph are the primary influence regulating naive T cell differentiation, be it active immunity or tolerance. How DCs achieve this regulation in vivo is poorly understood. Intestinal DCs are in direct contact with harmless or pathogenic luminal contents, but may also be influenced by signals from epithelial cells, macrophages, or other resident or immigrant cells. To understand the role of TLR7 and TLR8 in regulating intestinal DC function, we fed a TLR7/8 ligand (resiquimod (R-848)) to rats and mice and examined DC in pseudoafferent lymph (rat) and mesenteric lymph nodes (MLNs). Oral R-848 induced a 20- to 30-fold increase in DC output from the intestine within 10 h due to a virtually total release of lamina propria DCs. This resulted in an accumulation of DCs in the MLNs that in mice was completely TNF-alpha dependent. Surprisingly, intestinal lymph DCs (iL-DCs) released by R-848 did not up-regulate CD86, but did up-regulate CD25. In contrast, MLN-DCs from R-848-stimulated rats and mice expressed high levels of CD86. This DC activation in MLNs was dependent on type 1 IFNs. The major source of these rapidly released cytokines is plasmacytoid DCs (pDCs) and not classical DCs, because depletion of pDCs significantly reduces the R-848-stimulated increase in serum cytokine levels as well as the accumulation and activation of DCs in MLNs. These experiments show that TLR-mediated regulation of iL-DC functions in vivo is complex and does not depend only on direct iL-DC stimulation, but can be regulated by pDCs.

Relationships between distinct blood monocyte subsets and migrating intestinal lymph dendritic cells in vivo under steady-state conditions.

The origins of dendritic cells (DCs) are poorly understood. In inflammation, DCs can arise from blood monocytes (M(O)s), but their steady-state origin may differ, as shown for Langerhans cells. Two main subsets of M(O)s, defined by expression of different chemokine receptors, CCR2 and CX(3)CR1, have been described in mice and humans. Recent studies have identified the inflammatory function of CCR2(high)CX(3)CR1(low) M(O)s but have not defined unambiguously the origin and fate of CCR2(low)CX(3)CR1(high) cells. In this study, we show that rat M(O)s can also be divided into CCR2(high)CX(3)CR1(low)(CD43(low)) and CCR2(low)CX(3)CR1(high)(CD43(high)) subsets with distinct migratory properties in vivo. Using whole body perfusion to obtain M(O)s, including the marginating pool, we show by adoptive transfer that CD43(low) M(O)s can differentiate into CD43(high) M(O)s in blood without cell division. By adoptive transfer of blood M(O)s followed by collection of pseudoafferent lymph, we show for the first time that a small proportion of intestinal lymph DCs are derived from CCR2(low)CX(3)CR1(high)(CD43(high)) blood M(O)s in vivo under steady-state conditions. This study confirms one of the possible origins of CCR2(low)CX(3)CR1(high) blood M(O)s and indicate that they may contribute to migratory intestinal DCs in vivo in the absence of inflammatory stimuli.

Prions and their lethal journey to the brain.

Prion diseases are neurodegenerative conditions that cause extensive damage to nerve cells within the brain and can be fatal. Some prion disease agents accumulate first in lymphoid tissues, as they make their journey from the site of infection, such as the gut, to the brain. Studies in mouse models have shown that this accumulation is obligatory for the efficient delivery of prions to the brain. Indeed, if the accumulation of prions in lymphoid tissues is blocked, disease susceptibility is reduced. Therefore, the identification of the cells and molecules that are involved in the delivery of prions to the brain might identify targets for therapeutic intervention. This review describes the current understanding of the mechanisms involved in the delivery of prions to the brain.

Systemic autoimmune disease induced by dendritic cells that have captured necrotic but not apoptotic cells in susceptible mouse strains.

Systemic lupus erythematosus (SLE) is an autoimmune disorder of a largely unknown etiology. Anti-double-stranded (ds) DNA antibodies are a classic hallmark of the disease, although the mechanism underlying their induction remains unclear. We demonstrate here that, in both lupus-prone and normal mouse strains, strong anti-dsDNA antibody responses can be induced by dendritic cells (DC) that have ingested syngeneic necrotic (DC/nec), but not apoptotic (DC/apo), cells. Clinical manifestations of lupus were evident, however, only in susceptible mouse strains, which correlate with the ability of DC/nec to release IFN-gamma and to induce the pathogenic IgG2a anti-dsDNA antibodies. Injection of DC/nec not only accelerated disease progression in the MRL/MpJ-lpr/lpr lupus-prone mice but also induced a lupus-like disease in the MRL/MpJ-+/+ wild-type control strain. Immune complex deposition was readily detectable in the kidneys, and the mice developed proteinuria. Strikingly, female MRL/MpJ-+/+ mice that had received DC/nec, but not DC/apo, developed a 'butterfly' facial lesion resembling a cardinal feature of human SLE. Our study therefore demonstrates that DC/nec inducing a Th1 type of responses, which are otherwise tightly regulated in a normal immune system, may play a pivotal role in SLE pathogenesis.

How do DCs interact with intestinal antigens?

Recent evidence demonstrates that dendritic cells (DCs) can insert dendrites between the epithelial cells that form the barrier protecting the body from the gut contents. Although first observed almost a decade ago, this is a controversial area of DC biology and the physiological importance of this phenomenon is only now being clarified. A recent study by Niess and colleagues shows that this behaviour enables efficient sampling of both invasive and non-invasive bacteria and might enhance the ability of an organism to resist infections by a pathogenic strain of Salmonella.

Intestinal dendritic cell subsets: differential effects of systemic TLR4 stimulation on migratory fate and activation in vivo.

Dendritic cells (DC) present peripheral Ags to T cells in lymph nodes, but also influence their differentiation (tolerance/immunity, Th1/Th2). To investigate how peripheral conditions affect DC properties and might subsequently regulate T cell differentiation, we examined the effects of a potent DC-activating, TLR-4-mediated stimulus, LPS, on rat intestinal and hepatic DC in vivo. Steady-state rat intestinal and hepatic lymph DC are alpha(E2) integrin(high) (CD103) and include two subsets, signal regulatory protein alpha (SIRPalpha)(hi/low), probably representing murine CD8alphaalpha(-/+) DC. Steady-state lamina propria DC are immature; surface MHC class II(low), but steady-state lymph DC are semimature, MHC class II(high), but CD80/86(low). Intravenous LPS induced rapid lamina propria DC emigration and increased lymph DC traffic without altering SIRPalpha(high)/SIRPalpha(low) proportions. CD80/86 expression on lymph or mesenteric node DC was not up-regulated after i.v. LPS. In contrast, i.v. LPS stimulated marked CD80/86 up-regulation on splenic DC. CD80/86 expression on intestinal lymph DC, however, was increased after in vitro culture with TNF-alpha or GM-CSF, but not with up to 5 mug/ml LPS. Steady-state SIRPalpha(low) DC localized to T cell areas of mesenteric nodes, spleen, and Peyer's patch, whereas SIRPalpha(high) DC were excluded from these areas. Intravenous LPS stimulated rapid and abundant SIRPalpha(high) DC accumulation in T cell areas of mesenteric nodes and spleen. In striking contrast, i.v. LPS had no effect on DC numbers or distribution in Peyer's patches. Our results suggest that any explanation of switching between tolerance and immunity as well as involving changes in DC activation status must also take into account differential migration of DC subsets.

Dendritic cells and oral transmission of prion diseases.

Transmissible spongiform encephalopathies (scrapie, BSE, Kuru) develop as central nervous system (CNS) diseases after long incubation periods, and many of which may arise following the consumption of infected material. The infectious agent is thought to be a misfolded form (scrapie associated PrP (PrP(Sc))) of a normal host protein (cellular isoform of PrP (PrP(C))), which is relatively resistant to proteolytic degradation and which serves as a template, directing host prion protein (PrP) to accumulate in the misfolded form. Animal experiments have shown that CNS disease is preceded by a period in which the agent accumulates in secondary lymphoid organs (Peyer's patches (PP), lymph nodes, spleen), particularly follicular dendritic cells (FDCs) in the B cell areas of these organs. How the agent is transmitted from the intestinal lumen to the FDCs is largely unknown. Dendritic cells (DCs, cells quite distinct from FDCs) are cells that are specialised to acquire antigens from peripheral tissues and to transport them to secondary lymphoid organs for presentation to T and B lymphocytes. We have shown that DCs can acquire PrP(Sc) from the intestinal lumen and deliver it to mesenteric lymph nodes. In this review we discuss the different stages involved in the migration of PrP(Sc) from the intestine to FDCs and consider the different stages and barriers involved in this process. We conclude that transport of the causative agent, using PrP(Sc) as a biomarker, from the intestine to FDCs is a very inefficient process, which may help to account for the apparent low frequency of individuals who have consumed infected material that go on to develop clinical disease.