THC Suppressed Natural Killer Cell Activity That Normally Fights Tumor Cells | Research

The takeaway

In lab tests, THC suppressed human natural killer cell activity against a tumor cell line at concentrations as low as 5 micrograms/mL, with suppression depending on THC concentration and exposure duration.

Read this if you want to understand how THC affects immune cells that fight cancer in laboratory conditions.

NK cell activity suppressed at THC concentrations as low as 5 micrograms/mL

What the researchers found

Natural killer (NK) cells are immune cells that identify and destroy abnormal cells, including tumor cells. Researchers tested whether THC could affect this critical immune function.

THC was toxic to peripheral blood lymphocytes at 20 micrograms/mL but not at 10 micrograms/mL or below. At concentrations down to 5 micrograms/mL, THC inhibited NK cell activity against K562, a human tumor cell line.

The suppression of NK function depended on both the concentration of THC and how long the cells were exposed to it before encountering tumor targets. However, the suppression was independent of the ratio of NK cells to tumor cells, meaning more NK cells did not overcome the THC-induced impairment. Prostaglandins, which mediate some other forms of immune suppression, were not involved in this effect.

Why it matters

NK cells are a frontline defense against cancer cells. This study demonstrated that THC could suppress this defense in laboratory conditions, raising questions about whether cannabis use might affect cancer surveillance in living people.

The numbers in context

THC toxic at 20 micrograms/mL. Not toxic at 10 micrograms/mL or less. NK suppression observed down to 5 micrograms/mL. Suppression was dose-dependent and time-dependent.

How the study worked

In vitro study testing THC's effect on human natural killer cell function against K562 tumor cells. Variables included THC concentration, pre-incubation time, and effector-to-target cell ratios. Prostaglandin involvement was also assessed.

What this study cannot tell us

In vitro study using isolated cells in a dish, which does not account for the complex regulatory environment of the intact immune system. The THC concentrations tested may exceed physiologically relevant levels during typical cannabis use. The study tested isolated NK cells, not the coordinated immune response.

How to read the evidence

An in vitro laboratory study with human cells. Provides mechanistic data but cannot be directly applied to what happens in the human body.

When this study was published

Published in 1986. Understanding of the endocannabinoid system's role in immune regulation has expanded enormously since.

The bigger picture

This study contributed to the ongoing debate about cannabis and immune function. While in vitro studies consistently showed THC could suppress various immune functions, the concentrations used often exceeded what occurs in the bloodstream during typical cannabis use, making clinical relevance uncertain.

Questions still open

Do the THC concentrations that suppressed NK function in the lab correspond to levels achieved in cannabis users' blood? Does the immune system compensate for THC-induced NK suppression in living people? Would chronic cannabis users show reduced NK cell function?

Common questions

Does cannabis weaken the immune system's cancer defense?

In this lab study, THC suppressed NK cell activity against tumor cells. Whether this translates to reduced cancer surveillance in living cannabis users remains unclear.

Were the THC levels realistic?

The suppressive concentrations (5-10 micrograms/mL) are higher than typically found in cannabis users' blood, so the clinical relevance is uncertain.

Read the original research

Marijuana effects on immunity: suppression of human natural killer cell activity of delta-9-tetrahydrocannabinol.

International journal of immunopharmacology, 8(7), 741-5

View on PubMed ↗

Citation

Specter, S C; Klein, T W; Newton, C; Mondragon, M; Widen, R; Friedman, H. (1986). Marijuana effects on immunity: suppression of human natural killer cell activity of delta-9-tetrahydrocannabinol.. International journal of immunopharmacology, 8(7), 741-5.