Intra-epidermal vesicles

After 21 hours the increase in spongiosis gives the appearance of intra-epidermal vesicles (W. Jadassohn, Bujard and Brun, 1955). These histological lesions correspond to those observed in man. 

After 14 hours there are well formed spongiosis, occasionally intra-epidermal vesicles and an infiltrate which is rather moderate and composed of immature cells of connective tissue, small lymphocytes and eosinophils at times. 

Fourteen hours after the test, we observe spongiosis and intra-epidermic vesicles, as seen in the eczema caused by DNCB. However, the dermal infiltration is much more extensive with citraconic anhydride and contains lymphocytes and above all numerous eosinophils which invade the epidermis (Fig. 19). In eczema due to DNCB the infiltration is mainly by lymphocytes. 

If pure PA is applied to the flank and nipple of unsensitized guinea pigs, a light redness is observed after 14 hours. Under histological examination the lesions of the flank and nipple are numerous intra-epidermal vesicles, epidermal detachment, epidermal necrosis, dermal infiltrate with numerous eosinophils which also invade the epidermis. 

After 14 hours, the epidermal lesions are significant in certain places the epidermal cells are extremely swollen (pseudo-acanthosis ), elsewhere we see an atrophy of the epidermis and next to it, either a pseudo-acanthosis, or an acanthosis. Intra-epidermal vesicles are frequently seen (Fig. 20). 

It is not surprising to find intra- and perivascular eosinophils in the urticarial phase, as leucocytic infiltration with many eosinophils is characteristic of urticarial reactions in man (Berger and Lang, 1932 W. Jadassohn, 1932). However it is surprising that so many eosinophils (14 hours and more after the test) are seen at the same time as the eczematous epidermic lesions (spongiosis and intraepidermic vesicles). 

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