The immunomodulatory function evaluation test is a standardized battery of in vivo and in vitro assays used to substantiate immune-support claims for health foods, dietary supplements and functional ingredients. Performed by accredited third-party laboratories in accordance with national health food technical standards, GB toxicology principles and OECD guidelines, the test quantifies cellular immunity, humoral immunity, innate immunity and natural killer (NK) cell activity. This article explains the study design, core endpoints, testing methods, judgment criteria and typical applications of immune function assessment.
Technical Overview
The immunomodulatory function evaluation test is a systematic assessment designed to determine whether a test substance can enhance, regulate or restore immune system performance. It is most widely applied in the registration and functional substantiation of health foods claiming immune support, as well as in the screening of bioactive ingredients during product development.
In China, the evaluation follows the national technical standards for health food testing and assessment, which define the required test battery, dose design and judgment criteria for the immune function claim. Following the 2023 revision of the catalog of permissible health function claims, the claim is expressed as helping to enhance immune function, and human dietary trials are increasingly emphasized alongside animal data. Internationally, immune endpoints are also integrated into safety frameworks such as OECD Test Guideline 407 (28-day repeated dose toxicity) and OECD Test Guideline 443, which include immunological parameters as part of systemic toxicity screening.
The core test battery covers four functional domains:
- Cellular immunity (T-lymphocyte function)
- Humoral immunity (B-lymphocyte and antibody function)
- Non-specific, or innate, immunity (phagocytic activity)
- Natural killer (NK) cell activity
Supportive observations include body weight, food intake, clinical signs and immune organ indices (thymus and spleen weights relative to body weight). A positive conclusion generally requires significant improvement in at least one cellular or humoral immune endpoint, combined with significant improvement in at least one innate immunity or NK cell endpoint, without adverse effects on overall growth or other immune parameters. Studies are typically conducted in laboratories accredited to ISO/IEC 17025 and operating under Good Laboratory Practice (GLP) principles.
Testing Samples
Health Foods and Dietary Supplements
Finished dosage forms intended for immune-support claims, including capsules, tablets, granules, powders, oral liquids and beverages. The test article is prepared from the marketed or pilot-scale product, and dose levels are set relative to the recommended human daily intake after body-surface-area conversion.
Functional Ingredients and Bioactive Extracts
Representative materials include probiotics and postbiotics, yeast and cereal beta-glucans, lactoferrin, bovine colostrum, edible mushroom polysaccharides, Echinacea and elderberry extracts, spirulina, colostrum-derived immunoglobulins, vitamin and mineral premixes, and polysaccharide- or saponin-rich herbal preparations used in traditional medicine systems.
Novel Food Ingredients and Special Nutritional Foods
New food raw materials, foods for special medical purposes, maternal and infant nutrition products, and elderly nutrition formulations frequently require functional substantiation of immune benefits as part of their technical dossiers.
Research, Feed and Preclinical Materials
Candidate compounds under preclinical development, functional feed additives for livestock and aquaculture, veterinary nutraceuticals and fermented microbial products may also be evaluated using adapted versions of the same protocol.
Testing Items
The evaluation integrates general observations with a structured panel of immune endpoints:
- General parameters: body weight, food intake, clinical signs, survival
- Immune organ indices: thymus/body weight ratio and spleen/body weight ratio
- Cellular immunity: ConA-induced splenic T-lymphocyte proliferation (MTT assay); delayed-type hypersensitivity (DTH) response
- Humoral immunity: antibody plaque-forming cell (PFC) assay using sheep red blood cells (SRBC); serum hemolysin determination expressed as HC50
- Innate immunity: carbon particle clearance test; peritoneal macrophage phagocytosis of chicken red blood cells (phagocytic rate and phagocytic index)
- NK cell activity: lactate dehydrogenase (LDH) release assay against sensitive target cells
- Supplementary biomarkers (optional): serum IgG, IgM and IgA, secretory IgA, cytokines such as IL-2, IL-4, IL-6, IFN-gamma and TNF-alpha, lymphocyte subset profiling (CD3, CD4, CD8, CD19, CD16/CD56) by flow cytometry, and total/differential leukocyte counts
Testing Methods
Study Design and Dose Groups
Healthy SPF-grade mice, commonly BALB/c, ICR or Kunming strains aged 6 to 8 weeks (18 to 22 g), are randomized by body weight into a blank control group and at least three dose groups. Dose levels typically correspond to one, ten and thirty times the recommended human intake after conversion, with the high dose not exceeding the maximum tolerated dose established in prior safety studies. The test substance is administered by oral gavage once daily for at least 30 consecutive days, or by a design appropriate to the ingredient. A cyclophosphamide-induced immunosuppression model can be added to demonstrate restorative or protective activity in animals with suppressed immune function.
Cellular Immunity Assays
For lymphocyte proliferation, spleen cells are cultured with concanavalin A (ConA) as a T-cell mitogen, and proliferation is quantified by MTT colorimetry at 570 nm, yielding a stimulation index relative to unstimulated controls. For the delayed-type hypersensitivity test, animals are sensitized by abdominal application of DNFB and challenged on the ear; the degree of ear swelling reflects cell-mediated immune responsiveness.
Humoral Immunity Assays
In the Jerne plaque-forming cell assay, mice immunized with SRBC provide splenocytes that are embedded with SRBC and complement; antibody-secreting B cells generate hemolytic plaques that are counted microscopically. In the serum hemolysin test, serially diluted serum from SRBC-immunized animals is incubated with complement, and the degree of hemolysis is used to calculate the HC50 value, which reflects circulating antibody levels.
Innate Immunity Assays
In the carbon clearance test, diluted India ink is injected intravenously and blood is sampled at fixed intervals; the rate of carbon disappearance yields the phagocytic index, reflecting mononuclear phagocyte system function. In the macrophage phagocytosis test, peritoneal macrophages harvested ex vivo are incubated with chicken red blood cells, stained, and evaluated for phagocytic rate and phagocytic index.
NK Cell Activity Assay
Spleen effector cells are co-cultured with NK-sensitive target cells such as YAC-1 lymphoma cells at defined effector-to-target ratios. Cytotoxicity is quantified by LDH released from lysed target cells into the supernatant, and NK activity is calculated as a percentage of maximal release after correction for spontaneous release.
Supplementary Analyses and Statistics
Immunoglobulins and cytokines are measured by ELISA, and lymphocyte subsets are profiled by flow cytometry where required. Group data are compared using analysis of variance (ANOVA) with appropriate post-hoc tests, with statistical significance conventionally set at p less than 0.05. Dose-response relationships are evaluated as supporting evidence.
Judgment Criteria
A test substance is judged to support immune function when at least one cellular or humoral immune endpoint is significantly improved and, in addition, at least one innate immunity or NK cell endpoint is significantly improved. Results must show no significant depression of other immune parameters, no reduction in immune organ weights attributable to toxicity, and no adverse effect on body weight gain.
Applications
Immunomodulatory function evaluation data support a broad range of regulatory and commercial objectives:
- Registration and record-filing of health foods carrying immune-support claims in the Chinese market, where the evaluation forms part of the official functional test dossier
- Scientific substantiation of structure-function and immune health claims for dietary supplements in international markets
- Functional evidence packages for new food ingredient approvals and special nutritional food dossiers
- Research and development support, including formulation screening, dose-finding, strain selection for probiotics and comparative benchmarking
- Scientific publications, technical white papers and claim substantiation for marketing and label compliance defense
- Immunotoxicity screening integrated with GB 15193 food safety toxicology batteries for novel substances
FAQ
What animal model is used, and how long does the study take?
The standard model is healthy SPF mice (commonly BALB/c, ICR or Kunming strains), with oral administration for at least 30 consecutive days. Including acclimatization, dosing, immune challenge and endpoint assays, the in-life and analytical phases typically require 8 to 12 weeks.
How is a positive result determined?
A positive conclusion requires a significant improvement in at least one cellular or humoral immune endpoint plus at least one innate immunity or NK cell endpoint, with no adverse effects on growth, organ weights or other immune parameters. A clear dose-response relationship strengthens the conclusion.
Are human trials required?
For Chinese health food registration under the revised 2023 functional claim framework, human dietary trials are increasingly required or recommended for immune-related claims, building on animal efficacy data. Requirements should be confirmed against the current version of the applicable technical evaluation requirements before study initiation.
How much sample is needed for testing?
The required quantity depends on the dosage form, dose levels and group sizes, and must cover the full dosing period plus retention and retest allowances. Accredited third-party laboratories typically calculate exact requirements based on the confirmed study design.
Can the test evaluate recovery from immunosuppression?
Yes. A cyclophosphamide-induced immunosuppression model can be incorporated to assess whether the test substance restores suppressed cellular, humoral or innate immune function, which is particularly useful for ingredients positioned at immune-compromised or recovering populations.
Is GLP compliance necessary?
Studies intended to support regulatory submissions should be conducted under GLP principles in laboratories accredited to ISO/IEC 17025, ensuring data integrity, traceability and acceptance by review authorities.