Half hemolysis rate functional testing, commonly referred to as the HC50 (50% hemolytic value) assay, is a serological method used to evaluate humoral immune function by quantifying serum hemolysin activity against sheep red blood cells. This test is a core component of immune function evaluation for health foods, functional ingredients, and immunomodulatory products, providing quantitative evidence of antibody-mediated immune response. This article explains the technical principle, sample requirements, testing procedure, calculation method, and practical applications of HC50 functional testing.
Technical Overview
The half hemolysis rate (HC50) assay is a classical complement-dependent hemolysis test that measures the total hemolysin (anti-sheep red blood cell antibody) level in serum. In this assay, test animals are immunized with sheep red blood cells (SRBC), which stimulates B lymphocytes to produce specific anti-SRBC antibodies. When the collected serum is incubated with fresh SRBC and exogenous complement, the antigen-antibody-complement cascade is activated, resulting in erythrocyte lysis and hemoglobin release. The degree of hemolysis, measured spectrophotometrically, is directly proportional to the serum hemolysin concentration.
The HC50 value represents the serum dilution at which 50% of the standardized SRBC suspension is lysed, normalized against a complete-hemolysis reference. A higher HC50 value indicates a stronger humoral immune response. This method is recognized in functional evaluation protocols for health foods in accordance with the technical specifications for health food testing and evaluation and related GB standards, and it is typically performed by accredited third-party laboratories as part of a comprehensive immune function testing panel.
Testing Samples
Health Foods and Dietary Supplements
Finished health food products in various dosage forms, including tablets, capsules, softgels, oral liquids, powders, and granules, can be evaluated. Products intended to support immune function are the primary candidates for HC50 testing during registration or functional claim substantiation.
Functional Ingredients and Natural Extracts
Novel functional raw materials, botanical extracts, polysaccharides, probiotic preparations, peptide fractions, and other bioactive compounds with potential immunomodulatory activity can be screened using this assay during research and development.
Animal Serum Samples
Serum harvested from immunized laboratory rodents (typically mice) in preclinical studies constitutes the direct analytical matrix for the hemolysis measurement. Serum samples must be freshly prepared or properly stored under frozen conditions to preserve antibody and complement-related activity.
Testing Items
The core testing item is the serum half hemolysis value (HC50), which reflects the total level of anti-SRBC hemolysin antibody. HC50 determination is usually combined with other immune function endpoints to form a complete evaluation panel, including:
- Serum hemolysin level (HC50) determination for humoral immunity assessment
- Antibody-producing cell enumeration (plaque-forming cell assay)
- Delayed-type hypersensitivity reaction (footpad swelling test)
- Carbon clearance test for mononuclear-macrophage phagocytic function
- NK cell activity assay
- ConA-induced lymphocyte proliferation assay
- Splenocyte and immune organ index measurements
Testing Methods
Experimental Design and Immunization
Healthy mice within a defined body weight range (commonly 18 to 22 grams) are randomly assigned to control, low-dose, medium-dose, and high-dose groups, following the dose-setting principles of the applicable health food evaluation guidelines. After a period of sample administration (typically 30 to 45 days), each animal receives an intraperitoneal immunization with a standardized 2% SRBC suspension. Serum is collected four to five days after immunization.
Hemolysis Reaction Procedure
The collected serum is heat-inactivated and serially diluted in isotonic buffer. Aliquots of diluted serum are mixed with a defined volume of 2% SRBC suspension and freshly reconstituted guinea pig complement as the complement source. The reaction mixtures are incubated in a 37°C water bath for approximately 30 minutes to allow antibody-mediated, complement-dependent hemolysis to proceed. The reaction is then terminated by ice-bath cooling, and the samples are centrifuged to sediment intact erythrocytes.
Quantification and Calculation
The hemoglobin content in the supernatant is measured by UV-visible spectrophotometry at 540 nm. A complete-hemolysis reference tube, prepared by lysing the same SRBC volume in distilled water, establishes the 50% hemolysis benchmark. The HC50 value is calculated using the following relationship:
- HC50 = (absorbance of the sample tube / absorbance of the half-hemolysis reference tube) × serum dilution factor
Quality Control Measures
Reliable results depend on strict control of critical variables, including SRBC freshness and standardized cell concentration, verified complement activity, precise water bath temperature, consistent centrifugation conditions, and appropriate replicate measurements. Statistical analysis of HC50 values between the test groups and the negative control group is performed to determine significance.
Applications
HC50 functional testing serves multiple purposes across product development and regulatory compliance:
- Functional claim substantiation for immune-supporting health foods during product registration and filing
- Efficacy screening of immunomodulatory ingredients during early-stage research and development
- Comparative evaluation of formulation optimization and dosage selection
- Supporting data generation for scientific publications and technical dossiers
- Verification of immunomodulatory effects in preclinical laboratory studies
A positive immune function result generally requires that the HC50 value of at least one dose group is significantly higher than that of the control group, supported by a plausible dose-response trend across the tested concentrations.
FAQ
What is the difference between HC50 and CH50? HC50 measures antigen-specific serum hemolysin antibody levels produced in response to SRBC immunization and is used to evaluate humoral immune function of test substances. CH50 measures total complement activity in serum. Although both are complement-dependent hemolysis assays, they evaluate different components of the immune system.
How long does the complete HC50 test take? The full study, including the sample administration period, SRBC immunization, serum collection, and hemolysis assay, typically requires five to seven weeks depending on the study design and dosing duration.
What sample information should be provided for testing? Clients should provide product name, dosage form, recommended human intake, ingredient composition, sample quantity, and any special handling requirements so that the laboratory can design dose groups according to the relevant evaluation guidelines.
What factors can affect the accuracy of results? SRBC storage duration and concentration, complement freshness, incubation temperature, serum handling conditions, and animal health status are the main variables. Accredited third-party laboratories control these parameters through validated operating procedures to ensure reproducibility.
Is HC50 testing sufficient to claim immune-enhancing function? No. HC50 reflects only humoral immunity. A complete immune function evaluation should combine humoral, cellular, and nonspecific immunity endpoints, with multiple positive results required to support a comprehensive immune function claim.