Background: More information on the bioefficacy of carotenoids in foods ingested by humans is needed. Objective: We aimed to measure the time required for isotopic enrichment of β-carotene and retinol in serum to reach a plateau, the extent of conversion of β-carotene dissolved in oil with use of β-carotene and retinol specifically labeled with 10 ¹³C atoms, and the intraindividual variation in response. Design: Indonesian children aged 8–11 y (n = 35) consumed 2 capsules/d, 7 d/wk, for ≤10 wk. Each capsule contained 80 μg [12,13,14,15,20,12′,13′,14′,15′,20′-¹³C₁₀]β-carotene and 80 μg [8,9,10,11,12,13,14,15,19,20-¹³C₁₀]retinyl palmitate. Three blood samples were drawn per child over a period of ≤10 wk. HPLC coupled with atmospheric pressure chemical ionization liquid chromatography–mass spectrometry was used to measure the isotopic enrichment in serum of retinol with [¹³C₅]retinol and [¹³C₁₀]retinol and of β-carotene with [¹³C₁₀]β-carotene. The β-carotene in the capsules used had a cis-trans ratio of 3:1. Results: Plateau isotopic enrichment was reached by day 21. The amount of β-carotene in oil required to form 1 μg retinol was 2.4 μg (95% CI: 2.1, 2.7). The amount of all-trans-β-carotene required to form 1 μg retinol may be lower. Conclusions: The efficiency of conversion of this β-carotene in oil was 27% better than that estimated previously (1.0 μg retinol from 3.3 μg β-carotene with an unknown cis-trans ratio). The method described can be extended to measure the bioefficacy of carotenoids in foods with high precision, requiring fewer subjects than other methods.

An effective cytotoxic T lymphocyte (CTL) response against intracellular pathogens is generally accomplished by immense CTL expansion and activation, which can destroy infected cells. Vigorous immune responses can lead to activation of bystander CD8⁺ T cells, but the contribution from antigen-specific CTLs is not well understood. We found that CTLs secrete extracellular vesicles following antigen stimulation. These CTL-derived vesicles contain CTL proteins and exhibit markers and size profiles consistent with exosomes. Interestingly, further stimulation of CTLs with IL-12 impacts exosome size and leads to selective enrichment of certain exosomal proteins. More important, exosomes from IL-12-stimulated CTLs directly activated bystander naïve CD8⁺ T cells to produce interferon-γ (IFNγ) and granzyme B (GZB) in the absence of antigens, whereas control exosomes derived from antigen-stimulated CTLs did not. In addition, IL-12 induced exosomes are able to strengthen the effects of weak antigen stimulation on CTLs. Proteomic analysis demonstrates that IL-12 stimulation alters catalytic and binding activities of proteins in CTL exosomes. Our findings indicate that the biological function and morphology of exosomes secreted by CTLs can be influenced by the type of stimulation CTLs receive. Thus, a fully functional, ongoing, antigen-specific CTL response may influence bystander CD8⁺ T cells through secretion of exosomes.