MELISA

Key takeaways

MELISA belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect MELISA to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of MELISA from memory before moving on to harder problems.

Reference excerpt

MELISA (Memory Lymphocyte Immunostimulation Assay) is a blood test that detects type IV hypersensitivity to metals, chemicals, environmental toxins and molds. Type IV hypersensitivity reactions, particularly to nickel, are well established and may affect 20% of the population.

Mechanism The MELISA test measures type-IV delayed hypersensitivity reaction. Type-IV reactions are mediated by T-lymphocytes (or memory lymphocytes) that have had prior contact with a given allergen. This is in contrast to a type-I allergy, which is mediated by IgE antibodies and is often tested using an ELISA test. In genetically predisposed individuals, an ongoing exposure to allergens can induce type-IV hypersensitivity. The MELISA assay is a cell culture and requires live memory lymphocytes. Lymphocytes are isolated from a blood sample and cultured in an incubator for five days. A portion of the blood is kept intact (unexposed to allergens) to serve as a negative control. A second portion is exposed to a universal allergen, Pokeweed, to serve as a positive control. Finally, the blood is exposed to the suspected allergen/s in several different concentrations, to ensure that the conditions in vitro are as similar as possible to those in vivo. The lymphocyte reaction to each allergen is measured by two separate technologies: one based on the uptake of a radioactive isotope, 3H-thymidine, by dividing lymphocytes (proliferation); the other by cell staining and microscopy evaluation. The level of reactivity is measured as a Stimulation Index (SI), against the naïve lymphocytes from the unexposed sample (negative control). Viability and reactivity are determined by cell count as well as reaction to the positive control. MELISA is an optimised, standardised version of the lymphocyte transformation test (LTT) which was developed in the early 1960s to help identify allergies to drugs, metabolites and metals. The LTT for beryllium is now accepted as the gold standard for diagnosing berylliosis. MELISA differs from standard LTTs in several ways:

MELISA uses morphological screening to provide an additional level of accuracy. This ensures that non-hypersensitivity related cells (e.g. macrophages) are not included in the radioactively positive counts MELISA uses partially depleted monocytes to replicate the lymphocyte/monocyte balance in vivo MELISA utilizes a greater number of lymphocytes than other LTTs (1 million cells). As memory cells are relatively rare this higher concentration of lymphocytes ensures improved sensitivity.

Applications

Dentistry MELISA was further developed to help to assess the impact of hypersensitivity to metals used in dentistry. Hypersensitivity to dental metals may be associated with local oral reactions including oral lichen planus, stomatitis and ulceration. The frequency of metal-induced lymphocyte responses was examined in 3,162 dental patients in three European laboratories using the MELISA test. The patients suffered from local and systemic symptoms attributed to their dental restorations. The effect of dental metal removal was studied in 111 patients with metal hypersensitivity and symptoms resembling chronic fatigue syndrome (CFS). After consultation with a dentist, a subgroup of 111 patients who showed allergy to their dental metals replaced their restorations with non-metallic materials. Nickel was the most common sensitizer, followed by inorganic mercury, gold, phenylmercury, cadmium and palladium. As compared to lymphocyte responses in healthy subjects, the CFS group had significantly increased responses to several metals, especially to inorganic mercury, phenylmercury and gold. Following dental metal removal:

76% reported long-term health improvement 22% reported unchanged health 2% reported worsening of symptoms

Orthopaedics and surgery Type IV hypersensitivity to metals is common, particularly to nickel, however hypersensitivity related complications associated with metal implants are less frequently reported. Potential hypersensitivity complications include skin rashes, chronic joint pain, swelling, aseptic loosening, and joint failure. Many authors conclude that LTT-based blood tests like MELISA may be a better option for detecting systemic allergies from implants, while patch testing is better suited to detecting dermal hypersensitivity. They add that LTT based testing may also be a good option in cases of indeterminate hypersensitivity or in patients with joint failure of an unknown cause since it has higher sensitivity than patch testing Some surgeons and researchers suggest LTT testing prior to surgery in patients with suspected/self-reported metal allergy

Titanium hypersensitivity Titanium and its main alloy (Ti6Al4V) are generally seen as hypoallergenic options for arthroplasty and for dental implants. Although uncommon, with a prevalence estimated at between 0.6 and 6.3%, titanium hypersensitivity has been reported post-implantation with symptoms including impaired fracture healing, local eczema, pain, swelling, systemic dermatitis, implant loosening, and failure, all of which have been reported to resolve with implant removal and replacement with a non-titanium implant In spinal surgery, microscopic titanium particles are present in the tissues surrounding the implant. These particles activate macrophages that increase bone absorption and inflammatory reactions. Released nanoparticles will circulate in the body fluids, eventually accumulating in remote organs. Titanium has been shown to induce clinically relevant hypersensitivity which can be detected with MELISA testing. The accuracy of patch testing for titanium allergy, in particular, seems to be variable; the Mayo clinic failed to find any positive reactions to titanium in over a decade, despite several published cases of titanium allergy.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with MELISA

Start with the simplest possible case. Write down what MELISA claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to MELISA before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about MELISA ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of MELISA

In research: MELISA appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses MELISA in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: MELISA is common in secondary-school and first-year university syllabi. It links to neighbouring topics Allergology, Biochemistry detection reactions, Blood tests, so understanding it makes those chapters shorter.
In everyday life: Look for MELISA outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study MELISA in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what MELISA means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain MELISA out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is MELISA in simple terms?

MELISA (Memory Lymphocyte Immunostimulation Assay) is a blood test that detects type IV hypersensitivity to metals, chemicals, environmental toxins and molds. Type IV hypersensitivity reactions, particularly to nickel, are well established and may affect 20% of the population.

Why does MELISA matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study MELISA?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on MELISA.