Las lectinas son proteínas que se unen a azúcares con una elevada especificidad para cada tipo distinto. Su principal papel está en los fenómenos de reconocimiento, tanto a nivel molecular como celular. Por ejemplo, algunas bacterias utilizan lectinas para acoplarse a las células del organismo hospedador durante la infección. No se deben confundir con las glicoproteínas: las lectinas reconocen carbohidratos, mientras que las glicoproteínas están formadas en parte por ellos. Tampoco deben confundirse con las lecitinas que son moléculas de lípidos con la que no guardan ninguna relación.

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Lectins are carbohydrate-binding proteins, macromolecules that are highly specific for sugar moieties. Long before a deeper understanding of their numerous biological functions, the plant lectins, also known as phytohemagglutinins, were noted for their particular high specificity for foreign glycoconjugates (e.g. those of fungi, invertebrates, and animals). and used in biomedicine for blood cell testing and in biochemistry for fractionation. Lectins perform recognition on the cellular and molecular level and play numerous roles in biological recognition phenomena involving cells, carbohydrates, and proteins. Lectins also mediate attachment and binding of bacteria and viruses to their intended targets. For example, it is hypothesized that some hepatitis C viral glycoproteins attach to C-type lectins on the host cell surface (liver cells) for infection. Lectins may be disabled by specific mono- and oligosaccharides, which bind to ingested lectins from grains, legume, nightshade plants and dairy; binding can prevent their attachment to the carbohydrates within the cell membrane. Some lectins may be powerful toxins as for instance ricin, and others have been incorporated into genetically engineered crops to transfer traits, such as resistance to pests and resistance to herbicides.

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