Cold activation of complement

Amentoflavone ameliorates cold stress-induced inflammation in lung by suppression of C3/BCR/NF-κB pathways

Background

Cold stress, which may lead to local and systemic injury, is reported to be related to the immune system, especially the complement system. At present, the lack of effective treatment is a critical issue. Amentoflavone (AF), which can inhibit cold stress-induced inflammation in lung by multiple mechanisms, is the main therapeutic ingredient in plants of the genus Selaginella.

Results

In the current study, we found that cold could induce lung inflammation related to the complement system and its downstream pathways. AF treatment significantly inhibited lung inflammation from cold exposure. We presented evidence that AF can bind to complement component 3 (C3) to regulate inflammation-related pathways involving Lck/Yes novel tyrosine kinase (Lyn), protein kinase B (Akt), nuclear factor-κB (NF-κB) and immune factors. Moreover, 30 mg/kg of AF caused significantly greater improvement than 15 mg/kg in reducing the level of C3 in lung tissue.

Conclusions

AF can protect lung tissue from cold exposure. The protective effect may be achieved by inhibition of C3 and negative regulation of the B cell receptor (BCR)/NF-κB signaling pathways and high mobility group box 1 (HMGB1), which ultimately ameliorates the inflammatory response.

Preanalytical classical and alternative complement pathway activity loss

Introduction

Complement functional analyses provide insight into the integrity of the entire complement reaction cascade. These tests are suitable for investigating suspected complement deficiencies. Falsely reduced test outcomes may result from preanalytical instabilities of individual complement components. To generate rationale for this or potential alternative practices, this study aimed to extend the knowledge on the preanalytical stability of widely used tests to screen the complement system. We assessed the influence of time, temperature and EDTA on classical (CH50) and alternative pathway (AP50) functional assay test results.

Materials and methods

We used nephelometric (C3d) and immunofixation (C3c) techniques to support the investigation of the preanalytical phase of basic complement system activity tests. Quantitative determination of classical and alternative pathway function was performed with a haemolytic activity assay and a C5b-9 neo-epitope ELISA-based assay respectively. Blood of five healthy volunteers was sampled and complement components allowed to degrade under different conditions.

Results

CH50 and AP50 remain stable for approximately one week in serum samples incubated on ice. CH50 activity decreased almost twice as fast in EDTA plasma compared to serum at room temperature. AP50 activity contrastingly, decreased twice as slow in EDTA plasma compared to serum at room temperature.

Conclusion

Serum on ice remains the preferred specimen for functional complement analyses. In the absence of serum transported on ice, serum kept at room temperature (not exceeding 24h) is suitable for classical and alternative pathway analyses. For alternative pathway analyses specifically, the C3-stabilising effect of EDTA allows for the extended use of EDTA plasma (not over 4 days). In these conditions, at least 85% of baseline complement activity remains.

Foot temperature in diabetic polyneuropathy: innocent bystander or unrecognized accomplice?

AIM

To explore mechanisms by which temperature could influence the pathogenesis and symptoms of diabetic polyneuropathy.

METHODS

We conducted a literature review attempting to identify mechanisms by which diabetic polyneuropathy could be affected by temperature.

RESULTS

Cooling can theoretically hasten the progression of diabetic polyneuropathy through several different mechanisms. Specifically, cooling can enhance neuronal ischaemia, increase formation of reactive oxygen species, slow axonal transport, increase protein kinase C activity, and interfere with immune function. Short-term temperature fluctuations (both warming and cooling) can initiate and exacerbate neuropathic pain by causing neuronal hyperexcitability and functional deafferentation. Although normal fluctuations of distal extremity temperature may be sufficient for these effects, impaired thermoregulation may make the distal extremities more susceptible to temperature extremes. Eventually, a 'vicious cycle' may ensue, resulting in neuronal deterioration with further disruption of temperature regulation. Limited epidemiological data suggest a higher prevalence of diabetic polyneuropathy in populations living in colder locations, supporting our hypothesis.

CONCLUSIONS

Variations in foot temperature may play an important but as yet unrecognized role in the development and symptoms of diabetic polyneuropathy. Further basic and clinical research exploring this concept could help elucidate the natural history of diabetic polyneuropathy and lead to novel therapeutic strategies.

Hepatitis C virus-related liver damage is related to cold activation of complement

A high positivity of cold activation of complement has been reported in Japanese patients having hepatitis B virus-negative chronic hepatitis. Although the cause of cold activation of complement is unknown, the involvement of hepatitis C virus (HCV) has been suspected. We studied the positivity of cold activation of complement in 253 patients, including 93 patients with chronic hepatitis C infection who received 6MU natural interferon-alpha per day for 24 continuous weeks. Cold activation was positive in 38% of patients with chronic hepatitis C and in 46% of patients with liver cirrhosis C. We did not detect cold activation in asymptomatic HCV carriers; patients with chronic hepatitis B, liver cirrhosis B, or alcohol-related liver damage; or in the controls. Cold activation was also negative in HCV-RNA-negative patients who responded completely to interferon-alpha, and in HCV-RNA-positive patients who responded partially whose serum alanine transaminase levels were normalized after interferon treatment. In the patients who had a relapse of hepatitis C after interferon treatment, positivity of cold activation increased sharply. We conclude that HCV-associated liver damage is related to the development of cold activation of complement. Cold activation is useful for monitoring the response to interferon in patients with chronic hepatitis C infection.

Cold-dependent activation of complement: recognition, assessment, and mechanism

Cold-dependent activation of complement (CDAC) is a phenomenon characterized by low hemolytic complement activity in chilled serum. Complement component levels are normal when measured immunologically, and there is normal hemolytic activity in EDTA plasma or serum maintained at 37 degrees C. Little attention has been paid to CDAC except in Japan, and current unfamiliarity with it, even by clinical immunologists, can lead to confusion and unnecessary laboratory tests. A 66-year-old patient with a complex medical history is described whose complement tests showed abnormalities characteristic of CDAC. Evidence for classical complement pathway activation in the cold was obtained by CH50 measurements, by hemolytic C4 determinations, by C4a, C3a, and C4d generation, and by quantitating C1s-C1r-(C1 inhibitor)2 complexes. A good correlation was observed among these parameters. Cryoprecipitates were absent. CDAC activity has persisted for over 5 years and is greater at 13 than at 4 degrees C. Activation is ablated by heating at 56 degrees C and restored by the addition of C1 to the heated serum. Adsorption by streptococcal protein G-Sepharose and precipitation by 2.5% polyethylene glycol support the hypothesis that CDAC is caused by aggregated IgG. The CDAC factor(s) also induces complement activation in normal serum but has not interfered with Raji cell or C1q binding tests or with FACS analysis. More limited studies of a second individual experiencing CDAC yielded similar results.