Changes in serum and urinary potassium levels during profound hypothermia in man

Samples of blood were taken at five to 10-minute intervals during cooling, circulatory arrest, and rewarming in eight consecutive patients undergoing open cardiac surgery under profound hypothermia at nasopharyngeal and oesophageal temperatures of approximately 10°C. and the serum potassium levels were estimated. Urine samples were also collected from six of the eight patients and the total potassium excretion calculated per minute. It was found that there was a tendency for the serum potassium level to rise towards the end of cooling. A further more significant rise occurred during circulatory arrest, and on rewarming there was a pronounced fall of approximately 2·5 mEq./litre, the lowest level being reached at 27·5°C. Above 27·5°C. there was no further significant change in the serum potassium level. It is suggested that the acidosis which occurs during circulatory arrest and a depression in the function of the cell membrane at very low temperatures are at least partly responsible for the changes in serum potassium. Certainly the excretion of potassium in the urine does not account for them.     

Hepatitis C virus (HCV)-induced IgG-IgM rheumatoid factor (RF) complex may be the main causal factor for cold-dependent activation of complement in patients with rheumatic disease

A low serum complement level is commonly found in patients with rheumatic diseases. We evaluated 170 patients with such diseases to determine their serum levels of CH₅₀, C3 and C4 protein. Persistent hypocomplementaemia was found in 19 of those patients, particularly in those with systemic lupus erythematosus (SLE). Cold-dependent activation of complement (CDAC) was demonstrated in nine of the 19 (47.4%), and six of the nine patients demonstrated infection with HCV (66.7%). The nine patients that exhibited CDAC had nearly normal haemolytic complement activity when the sera were separated either at 37°C or in EDTA-treated plasma. Conversely, it markedly decreased, even to the point of being immeasurable, when the sera were separated at 4–21°C. No significant deficiency in C3 and C4 protein levels was found in these patients. Clinical parameters other than levels of anti-HCV antibody, transaminase, and RF were not influenced by CDAC. In an attempt to isolate the causal factor for CDAC, we isolated IgG fractions from the CDAC patients by using a protein G column, in which case precipitates were collected from the eluates. The precipitates were mixed with normal serum and incubated at 4–21°C for 18 h. A decrease in the level of CH₅₀ in normal serum was observed, which predominated (P<0.001) when precipitates from HCV-infected patients were used. This indicated CDAC was possibly interrelated to the precipitates of such patients. This precipitate was proved to contain IgM besides IgG. It is therefore possible that an HCV-related IgG complex or an IgG-IgM RF complex may be formed at low temperature and be involved in activating the complement system in vitro.     

IgA/IgC cryoglobulinaemia with vasculitis

A mixed IgA/IgG cryoglobulin complex was found in the serum of a 61-year-old man suffering from rheumatoid arthritis, Raynaud's phenomenon and vascular purpura. The purified complex was progressively insoluble at temperatures below 37°C. Reversible loss of cryoprecipitability was seen in conditions of extreme pH, in concentrated urea solutions and in 2-mercaptoethanol. Inactivation of complement at 56°C did not affect cryoprecipitability. The complex contained no complement and showed no anticomplementary activity. Analytical ultracentrifugation of the cryoglobulin at 37°C showed 7S and 11S components present in equal concentration.

The component immunoglobulins of the complex were separated by anion exchange chromatography at 37°C. Crossmixing studies with purified normal immunoglobulins indicated that the patient's IgA component was essential for cryoprecipitability of the complex. RA latex tests for anti-IgG activity at 37°C showed strong agglutination with both cryoglobulin complex and the isolated IgA component; this protein was found to be monoclonal with type K light chains.

Vasculitis, induced by skin testing the patient with his own plasma and isolated cryoglobulin was found to be histologically indistinguishable from that occuring spontaneously; reduction of symptoms paralleled reduction of cryoglobulin on treatment. These observations strongly support the hypothesis that the cryoglobulin complex is responsible for the patient's vasculitis.

     

Sensitivity of SARS‐CoV‐2 to different temperatures

This study was designed to investigate the sensitivity of SARS‐CoV‐2 to different temperatures, to provide basic data and a scientific basis for the control of COVID‐19 epidemic. The virus was dispersed in 1 mL basal DMEM medium at a final concentration of 10^3.2 TCID₅₀/mL and then incubated at 4, 22, 30, 35, 37, 38, 39 and 40°C for up to 5 days. The infectivity of residual virus was titrated using the Vero E6 cell line. The results showed that the virus remained viable for 5 days at 4°C, and for 1 day only at 22 and 30°C. We found that the infectivity of the virus was completely lost after less than 12 hours at 37, 38 and 39°C, while at 40°C, the inactivation time of the virus was rapidly reduced to 6 hours. We show that SARS‐CoV‐2 is sensitive to heat, is more stable at lower temperatures than higher temperature, remains viable for longer at lower temperatures, and loses viability rapidly at higher temperatures.     

Assessing the Validity of Aural Thermometry for Measuring Internal Temperature in Patients With Exertional Heat Stroke

ContextThe use of aural thermometry as a method for accurately measuring internal temperature has been questioned. No researchers have examined whether aural thermometry can accurately measure internal body temperature in patients with exertional heat stroke (EHS).ObjectiveTo examine the effectiveness of aural thermometry as an alternative to the criterion standard of rectal thermometry in patients with and those without EHS.DesignCross-sectional study.SettingAn 11.3-km road race.Patients or Other ParticipantsA total of 49 patients with EHS (15 men [age = 38 ± 17 years], 11 women [age = 28 ± 10 years]) and 23 individuals without EHS (10 men [age = 62 ± 17 years], 13 women [age = 45 ± 14 years]) who were triaged to the finish-line medical tent for suspected EHS.Main Outcome Measure(s)Rectal and aural temperatures were obtained on arrival at the medical tent for patients with and those without EHS and at 8.3 ± 5.2 minutes into EHS treatment (cold-water immersion) for patients with EHS.ResultsThe mean difference between temperatures measured using rectal and aural thermometers in patients with EHS at medical tent admission was 2.4°C ± 0.96°C (4.3°F ± 1.7°F; mean rectal temperature = 41.1°C ± 0.8°C [106.1°F ± 1.4°F]; mean aural temperature = 38.8°C ± 1.1°C [101.8°F ± 2.0°F]). Rectal and aural temperatures during cold-water immersion in patients with EHS were 40.4°C ± 1.0°C (104.6°F ± 1.8°F) and 38.0°C ± 1.2°C (100.3°F ± 2.2°F), respectively. Rectal and aural temperatures for patients without EHS at medical tent admission were 38.8°C ± 0.87°C (101.9°F ± 1.6°F) and 37.2°C ± 1.0°C (99.1°F ± 1.8°F), respectively.ConclusionsAural thermometry is not an accurate method of diagnosing EHS and should not be used as an alternative to rectal thermometry. Using aural thermometry to diagnosis EHS can result in catastrophic outcomes, such as long-term sequelae or fatality.     

Thermal regulation of the immune response in South American toads (Bufo marinus)

Thermal regulation of the immune response was studied in toads following single injections of bacteriophage f2. The immune response was markedly inhibited in animals kept at 15° as compared to the controls (25°). The appearance of serum antibodies was delayed in animals kept at 15° for the first post-immunization week but their peak antibody levels were similar to those in toads maintained at 25° throughout. Transfer of animals from 25° to 15° 2 weeks after immunization only temporarily depressed the serum antibody levels but caused a marked delay in conversion from heavy to light antibodies.

Our results are in keeping with the hypothesis that lowered environmental temperatures inhibit a variety of metabolic processes which may be concerned with the utilization of antigen and/or the synthesis of antibodies.

     

The incidence of cryoglobulinaemia as determined by a turbidimetric method

The incidence of cryoglobulinaemia was determined in 34 normal persons and in 56 sera from 52 patients with miscellaneous disorders. The turbidity of a sample of serum after 18 hours' refrigeration at 4°C. was compared with a sample of the same serum incubated at 38°C. for the same period of time. All refrigerated sera showed a greater turbidity than incubated sera. The abnormal sera showed a high degree of statistically significant correlation between total protein, γ globulin, and the amount of cryoglobulinaemia. There was no significant correlation between cryoglobulinaemia and the age and sex of individuals or any of the other protein fractions. The results suggest that some degree of cryoglobulinaemia is of almost universal occurrence in various unrelated disorders and that this tendency to precipitate out in the cold is a characteristic of the γ globulin group of proteins, especially when present in excess.     

Autoantibody Production in Rabbits: II. Organ-Specific Autoantibody in Rabbits Injected with Rat Tissues

The sera of rabbits injected with rat liver, kidney, heart, muscle, spleen and brain in Freund's complete adjuvant fixed complement with rabbit tissue. This complement-fixing activity was attributed to autoantibodies which were able to fix complement in vitro with the tissue of the rabbit in which they occurred. Absorption, gel diffusion and antibody and antigen titrations indicated that some of the anti-liver, anti-kidney, anti-heart, anti-muscle and anti-brain sera contained organ-specific autoantibody. The sera also contained autoantibody reacting with widely distributed antigen(s), which was relatively labile at 65°. The anti-kidney and anti-brain sera reacted with distinct antigens which were extracted from rabbit kidney and brain with a mixture of chloroform and methanol. The natural autoantibody of Kidd and Friedewald was usually labile at 65° and behaved like a macroglobulin on sucrose gradient centrifugation. Sera taken 1 week after immunization with rat tissue contained heat-labile macroglobulin antibody. However, sera taken 1 month after immunization also contained small molecular weight antibody which was stable at 65°.     

C1q rs292001 polymorphism and C1q antibodies in juvenile lupus and their relation to lupus nephritis

C1q deficiency is related strongly to systemic lupus erythematosus (SLE), but very few and inconsistent studies explored the single nucleotide polymorphisms of the C1q gene in relation to juvenile SLE (jSLE) and lupus nephritis (LN). The objective of this study was to analyse whether C1q rs 292001 polymorphism is associated with SLE and disease phenotype, especially nephritis, and to investigate the relation between this polymorphism and clinical data, treatment outcome, serum level of C1q protein and antibodies. Typing of C1q rs292001 polymorphism using restriction fragment length polymorphism and measuring serum levels of C1q protein and antibodies by enzyme-linked immunosorbent assay (ELISA) were performed for 130 children with SLE and 208 healthy controls. The A allele of C1q rs292001 was associated with jSLE and LN (P = 0·005 and 0·013, respectively) and the AA genotype was associated with jSLE (P = 0·036). Low serum levels of C1q protein were found in jSLE and LN (P < 0·001 and 0·009, respectively), and these levels were increased after treatment in patients with LN (P = 0·009) and active renal disease (P = 0·027). Higher titres of C1q antibodies were found in patients with LN (P = 0·015) and correlated negatively with C1q protein level (P < 0·001) and patient age (P = 0·04). The A allele and AA genotype of C1q rs292001 can be considered a susceptibility risk factor and the GG genotype could be considered protective for jSLE and LN in the studied cohort of Egyptian children. Decreased serum levels of C1q protein and increased titres of C1q antibodies may be involved in the pathogenesis of jSLE, especially LN.     

Effects of storage conditions on the stability of serum CD163, NGAL,HMGB1 and MIP2

Background: Several cytokines have been involved in the diagnosis and prognosis for the pathogenesis and severity of chronic hepatitis B (CHB) such as cluster of differentiation 163 (CD163), neutrophil gelatinase-associated lipocalin (NGAL), high-mobility group box 1 (HMGB1) and macrophage inflammatory protein-2 (MIP-2). Nevertheless, the stability and reliability of these cytokines can be greatly influenced by handling and storage processes. Methods: In this study, potential utility of serum samples of a CHB cohort was evaluated to investigate several processes that might impact cytokine profiles such as temperature, storage time and number of freeze-thaw cycles. Blood samples collected from 100 patients with CHB were separated immediately and divided into two groups. In one group, samples (n=50) stored at -80°C were subject to 1-3 freeze-thaw cycles. In the other group, samples (n=50) were stored at 4°C and 25°C for 3 h, 9 h, 24 h, 48 h, 72 h, and 7 d time points, respectively. To assess the influence of different storage conditions on cytokines, the levels of CD163, NGAL, HMGB1 and MIP-2 were measured using enzyme-linked immunosorbent assays (ELISA) kits. Results: No significant differences of these four cytokines after 1-3 repeated freeze-thaw cycles. Significant differences of NAGL levels were seen between 9 h and 7 d (P<0.05), and also in HMGB1 at 25°C, while the other cytokines were relatively stable at the two storage temperatures over the various time points. Conclusion: This study indicated that these four cytokines remained stable within three freeze-thaw cycles and 7 d at 4°C. No perceptible effects on CD163 and MIP-2 levels were presented under the storage condition of 7 d at room temperature, whereas the degradation of NGAL and HMGB1 were notable.     

Enterococcus faecalis adhesin, ace, mediates attachment to extracellular matrix proteins collagen type IV and laminin as well as collagen type I

Adhesin-mediated binding to extracellular matrix (ECM) proteins is thought to be a crucial step in the pathogenic process of many bacterial infections. We have previously reported conditional adherence of most Enterococcus faecalis isolates, after growth at 46°C, to ECM proteins collagen types I and IV and laminin; identified an E. faecalis-specific gene, ace, whose encoded protein has characteristics of a bacterial adhesin; and implicated Ace in binding to collagen type I. In this study, we constructed an ace disruption mutant from E. faecalis strain OG1RF that showed marked reduction in adherence to collagen types I and IV and laminin when compared to the parental OG1RF strain after growth at 46°C. Polyclonal immune serum raised against the OG1RF-derived recombinant Ace A domain reacted with a single ~105-kDa band of mutanolysin extracts from OG1RF grown at 46°C, while no band was detected in extracts from OG1RF grown at 37°C, nor from the OG1RF ace mutant grown at 37 or 46°C. IgGs purified from the anti-Ace A immune serum inhibited adherence of 46°C-grown E. faecalis OG1RF to immobilized collagen type IV and laminin as well as collagen type I, at a concentration as low as 1 μg/ml, and also inhibited the 46°C-evoked adherence of two clinical isolates tested. We also showed in vitro interaction of collagen type IV with Ace from OG1RF mutanolysin extracts on a far-Western blot. Binding of recombinant Ace A to immobilized collagen types I and IV and laminin was demonstrated in an enzyme-linked immunosorbent assay and was shown to be concentration dependent. These results indicate that Ace A mediates the conditional binding of E. faecalis OG1RF to collagen type IV and laminin in addition to collagen type I.     

Assessment of Hepatitis B Virus DNA Stability in Serum by the Chiron Quantiplex Branched-DNA Assay

Quantification of hepatitis B virus (HBV) DNA in serum is used to establish eligibility for treatment and to monitor therapeutic response. With the trend toward centralized testing, defining the conditions that preserve sample integrity is of paramount importance. We therefore evaluated the stability of HBV DNA in 26 previously frozen (PF) and 5 fresh, never previously frozen serum specimens. PF specimens, covering a 3-log₁₀ HBV DNA dynamic range, were thawed and stored at −70, 4, 23, 37, and 45°C (±1.5°C) for 0, 24, 72, and 120 h (±2 h) and were refrozen at −70°C prior to testing. Five fresh specimens were split into two groups. Both group FG1 and group FG2 specimens were handled as described above; however, group FG1 specimens were subsequently maintained at 4°C and were never frozen prior to testing. Linear regression analysis of PF specimens demonstrated no significant HBV DNA degradation at ≤4°C over 5 days; however, HBV DNA levels decreased by 1.8, 3.4, and 20% per day at 23, 37, and 45°C, respectively. Three independent statistical methods confirmed that the probability of specimen failure, defined as a loss of 20% or more of HBV DNA and/or coagulation of serum, was lowest at ≤4°C and increased with temperature. Because only 10 to 20% of individual patient specimens demonstrated losses of HBV DNA of ≥20% at 23 or 37°C, sufficient numbers of serum specimens must be evaluated to determine overall statistical trends. In conclusion, HBV DNA integrity in separated serum specimens is preserved for at least 5 days when the specimens are stored at −70 or 4°C.     

Analysis of heart rate control to assess thermal sensitivity responses in Brazilian toads

In anurans, changes in ambient temperature influence body temperature and, therefore, energy consumption. These changes ultimately affect energy supply and, consequently, heart rate (HR). Typically, anurans living in different thermal environments have different thermal sensitivities, and these cannot be distinguished by changes in HR. We hypothesized that Rhinella jimi (a toad from a xeric environment that lives in a wide range of temperatures) would have a lower thermal sensitivity regarding cardiac control than R. icterica (originally from a tropical forest environment with a more restricted range of ambient temperatures). Thermal sensitivity was assessed by comparing animals housed at 15° and 25°C. Cardiac control was estimated by heart rate variability (HRV) and heart rate complexity (HRC). Differences in HRV between the two temperatures were not significant (P=0.214 for R. icterica and P=0.328 for R. jimi), whereas HRC differences were. All specimens but one R. jimi had a lower HRC at 15°C (all P<0.01). These results indicate that R. jimi has a lower thermal sensitivity and that cardiac control is not completely dependent on the thermal environment because HRC was not consistently different between temperatures in all R. jimi specimens. This result indicates a lack of evolutive trade-offs among temperatures given that heart rate control at 25°C is potentially not a constraint to heart rate control at 15°C.     

Fusion of Chlamydia trachomatis-Containing Inclusions Is Inhibited at Low Temperatures and Requires Bacterial Protein Synthesis

The human pathogen Chlamydia trachomatis is an obligate intracellular bacterium with a unique developmental cycle. Within the host cell cytoplasm, it resides within a membrane-bound compartment, the inclusion. A distinguishing characteristic of the C. trachomatis life cycle is the fusion of the chlamydia-containing inclusions with each other in the host cell cytoplasm. We report that fusion of inclusions does not occur at 32°C in multiple mammalian cell lines and with three different serovars of C. trachomatis. The inhibition of fusion was inclusion specific; the fusion with sphingolipid-containing secretory vesicles and the interaction with early endosomes were unaffected by incubation at 32°C. The inhibition of fusion of the inclusions was not primarily the result of delayed maturation of the inclusion, as infectious progeny was produced in host cells incubated at 32°C, and the unfused inclusions remained competent to fuse up to 48 h postinfection. The ability to reverse the inhibition of fusion by shifting the infected cells from 32 to 37°C allowed the measurement of the rate and the time of fusion of the inclusions after entry of the bacteria. Most significantly, we demonstrate that fusion of inclusions with each other requires bacterial protein synthesis and that the required bacterial protein(s) is present, but inactive or not secreted, at 32°C.     

Role of lymphocyte activation products (LAP) in cell-mediated immunity. I. Preparation and partial purification of guinea-pig LAP

Partial purification of soluble products of guinea-pig lymphocyte activation (LAP) was undertaken by fractional precipitation with ammonium sulphate, ion-exchange and Sephadex chromatography, and by immune precipitation of inducing antigen and of contaminating serum protein. During these purification steps the activity of macrophage migration-inhibition factor (MIF) was concentrated up to 1300-fold and separated from inducing antigen and serum protein. An endpoint assay was devised for expressing antigen-induced MIF activity of LAP fractions as weights of material giving 30% inhibition of migration (MI₃₀ doses).

MIF activity precipitated between 50% and 80% saturated ammonium sulphate and eluted from DEAE-cellulose at pH 7·9 at intermediate salt concentrations (0·03–0·2 M phosphate). On Sephadex gel filtration MIF activity was concentrated in fractions of molecular weight range 56,000–82,000 with a smaller amount of activity eluting from 20,000–56,000. After immune precipitation of extraneous protein and elution from DEAE-cellulose, LAP material was found to have an MI₃₀ dose of 0·4 μg.

Materials representative of antigen and serum protein-depleted MIF were selected for intralymphatic injection in order to determine whether MIF-rich LAP fractions were able to induce paracortical distension in guinea-pig lymph nodes (see following paper).

     

Further attempts to characterize the normal incomplete cold antibody

Attempts at eluting the normal incomplete cold (n.i.c.) antibody from sensitized red cells or red cell stroma, using standard methods, were unsuccessful; thus the antibody could not be detected in the eluates obtained by heating at 56° or 37° or by dissociation at acid pH. The n.i.c. antibody was partially eluted from sensitized red cells only when elution was carried out at 37° into serum instead of saline.

Elution of the antibody from dextran (Sephadex G-200)—n.i.c. antibody complex formed at 0° was also achieved using a 15 per cent NaCl solution at 37°.

Since it has been shown that red cells sensitized with the n.i.c. antibody are not agglutinated by anti-γG, anti-γA or anti-γM-globulin sera, an attempt at producing an antibody specifically reacting with the n.i.c. antibody was made by injecting into a rabbit the eluate obtained from zymosan—n.i.c. antibody complex. The immune serum was found to inhibit the n.i.c. antibody activity when added to normal serum and to interfere with the property of normal serum requiring the properdin system.

In the present work it is also confirmed that the antibody is not associated with γG or γM-globulin; thus adult and cord sera and one serum from a patient with severe hypogammaglobulinaemia were fractionated with zone electrophoresis or DEAE-cellulose chromatography and it was found that the antibody was not present in the fractions containing the bulk of γG or γM-globulin.

     

The relation between spontaneous activity, metabolic rate and the 24 hour cycle in mice at different environmental temperatures

1. Oxygen consumption rates and levels of spontaneous activity were recorded simultaneously for mice, both singly and in groups, over 24 hr periods at temperatures ranging from 8 to 37° C.

2. There was marked 24 hr variation in both metabolic rate and activity, with maxima during the night; the amplitude of the variation diminished at the lower environmental temperatures.

3. At 28-33° C environmental temperatures, increased activity was associated with an increased oxygen consumption rate.

4. At 8 and 15° C, increased activity was accompanied by only a small increase in oxygen consumption.

5. These results show that thermogenesis from spontaneous activity can take the place of thermoregulatory heat production in the cold.

     

Effect of incubation temperature on mitogen responses of lymphocytes from adult peripheral blood and from cord blood

Lymphocytes from normal adults, when cultured with phytohaemagglutinin (PHA) or Concanavalin A (Con A) at 39°C, showed an enhancement and earlier onset of ³H-thymidine incorporation compared with cultures incubated at 37°C. In contrast, the peak responses of cord blood lymphocytes incubated at either 35°C or 39°C did not differ significantly from those incubated at 37°C. Cultures of adult lymphocytes showed an exponential rise and fall in ³H-thymidine incorporation, which was much more rapid at 39°C than at 37°C. However, the kinetics of thymidine incorporation into mitogen-stimulated cord blood lymphocytes incubated at 39°C were similar to those at 37°C. The following results suggested that temperature acted predominantly on the proliferative phase of the transformation response. Firstly, by inhibiting binding of Con A using methyl-α-D-mannopyranoside, it was found that activation of adult lymphocytes took place within the same time period at both 39°C and 37°C. Secondly, cultures incubated at 37°C for 3 days, and labelled for 4 hr at either 37°C or 39°C showed no significant difference in ³H-thymidine uptake, whereas cultures incubated at 39°C for 3 days, and labelled for 4 hr at 37°C showed significantly higher responses than those both incubated and labelled at 37°C. Thirdly, the major increase in thymidine uptake occurred after incubation at 39°C for the second and third days of culture. These findings were consistent with a shortening of the cell cycle at the higher temperature. Thus, the failure of cord blood lymphocytes to show increased thymidine uptake after incubation at 39°C apparently reflects an insensitivity to temperature of certain of the metabolic pathways involved in cell replication in the neonate.     

Differences in interaction between immune complexes and complement receptors in serum and cerebrospinal fluid

Antigen—antibody complexes (Ag—Ab), prepared from ¹²⁵I-radiolabelled bovine serum albumin (BSA) and guinea-pig antibody, were (1) pre-incubated at 37°C for 30 min with serum or cerebrospinal fluid (CSF) in different proportions and then reacted with cells, (2) incubated at 37°C directly with cells suspended in serum or CSF for different time periods, or (3) bound to cells (following incubation with serum in optimal proportions) and the cell-bound immune complexes (IC) incubated with serum or CSF at 37°C for different time periods. When Ag—Ab were pre-incubated with serum or CSF and reacted with unfractionated blood cells or mononuclear cells, binding decreased as serum to Ag—Ab proportion was increased above 1:16, but increased as CSF to Ag—Ab proportion was increased. When serum diluted 200-fold (to approximate the protein concentration of CSF) was used in place of undiluted serum, serum-mediated binding paralleled CSF-mediated binding. Inactivation of serum, CSF, and 1:200 serum in different ways and substitution of human red blood cells (RBC) (known to possess C3b receptors) or sheep RBC (known not to possess C3b receptors) demonstrated that binding was to C3b receptors. Addition of CSF to serum did not alter serum-mediated binding. When Ag—Ab were incubated directly with unfractionated blood cells suspended in serum or CSF, binding increased rapidly in serum, reaching a maximum within 2—4 min, and IC then rapidly dissociated, whereas binding increased gradually in CSF and IC remained associated with cells. When serum diluted approximately 100-fold was used in place of undiluted serum, kinetics of serum-mediated interaction approached that of CSF-mediated interaction. When IC were bound to Raji cells or human RBC and the cell-bound IC incubated in serum or CSF, > 85% of IC dissociated in serum after 30 min, but no dissociation occurred in CSF. Dilution of serum > 1:16 and > 1:64 abolished dissociation from the two cell types, respectively. These results indicate that CSF mediates binding of IC to complement receptors on cells but lacks the activities of serum which convert IC into a non-binding state.