Allergenicity and cross-reactivity of buffalo grass (Stenotaphrum secundatum)

In the subtropical climate of South Africa, grasses of the subfamily Panicoideae are predominant. Bermuda grass has previously been shown to be an important local allergen, and immunoglobulin E (IgE) epitopes of Bermuda grass extracts are known to be distinct from those of the Pooid pollen extracts. Following our demonstration of sensitivity in 43% of patients grass-allergic to the Panicoid, Kikuyu grass, we have studied the closely related buffalo grass, Stenotaphrum secundatum, indigenous to the Western Cape region, the east coast of Africa and the oceanic islands such as Mauritius; and Eragrostis, another common indigenous grass with a wide distribution.

To partially characterise the allergens of buffalo pollen, and examine its immunological relationships with local common grasses such as Eragrostis and Kikuyu.

Grass-allergic patients were evaluated clinically, and skin prick tests (SPTs) and radio-allergosorbent tests (RASTs) to Bermuda and grass mix were performed. Sera of timothy grass-sensitive patients from Belgium were also included in this study. Pollen extract from buffalo grass was characterised by specific IgE binding by means of immunoblotting and enzyme-linked immunosorbent assay (ELISA). Cross-reactivity between the grasses was studied by means of inhibition of IgE binding.

More than 90% of grass-sensitive patients were found to have IgE antibodies to Buffalo and Eragrostis pollen. Inhibition of ELISA and immunoblots revealed that extracts of these grass pollens could significant inhibit IgE binding to the local grass pollens, Kikuyu, buffalo, Eragrostis and Bermuda on solid phase, but 100% inhibition was never achieved, indicating that cross-reactive but also unique epitopes are present. We also identified a subset of patients with negative RASTs to Bermuda, and minimal inhibition by Bermuda pollen extract.

Buffalo and Eragrostis are important aeroallergens in the Cape, dispersed during the long dry, windy summer. Our data suggest that the local grasses are major sensitisers, and that South African diagnostic panels should include extracts of buffalo and Eragrostis grasses.