Sixteen eligible cat-allergic participants will be accrued in the study. Eight participants who have been on subcutaneous immunotherapy (SCIT) at maintenance dosing for at least 1 year will be assigned to the SCIT cohort, and 8 participants who have never been on cat immunotherapy will be assigned to the No immunotherapy (IT) cohort. Participants will undergo intradermal cat allergen challenge in bilateral upper arms at baseline (Day 1), will undergo axillary lymph node and peripheral blood sampling at Day 4, and axillary lymph node, peripheral blood, and adenoid and nasal sampling at Week 3.

The primary objective is to determine the number of analyzable cells from axillary lymph node fine-needle aspiration 3 days and 3 weeks after intradermal cat allergen challenge in two cohorts of cat-allergic participants: those undergoing cat allergen immunotherapy and those who are not receiving this treatment

Inclusion Criteria:

1. Participant must be able to understand and provide informed consent
2. A clinical history of moderate to severe rhinoconjunctivitis symptoms caused by cat exposure, such that exposure is currently, or was historically to the initiation of treatment, interfering with usual daily activities or with sleep, as defined according to the ARIA classification of rhinitis
3. Skin prick test wheal greater than or equal to 5 mm to standardized cat extract or cat-specific IgE greater than or equal to 0.7 kU/L obtained within 5 years of screening. These can be obtained from medical records if available from the prior 5 years, or at the screening visit if not
4. Female participants of childbearing potential must have a negative pregnancy test at the screening visit prior to performing study procedures
5. For participants in the Subcutaneous Immunotherapy (SCIT) cohort, the following inclusion criterion applies as well: A history of at least 1 year of maintenance subcutaneous allergen immunotherapy to cat, with currently ongoing immunotherapy treatments at least every 6 weeks

Exclusion Criteria:

1. Inability or unwillingness of a participant to give written informed consent or comply with study protocol

2. Current household exposure to cat or regular occupational exposure to cat

3. For participants in No immunotherapy (IT) cohort, any previous immunotherapy treatment with cat allergen

4. For participants in No IT cohort, any current treatment with any form of allergen immunotherapy

5. A history of grade 4 anaphylaxis due to any cause as defined by the WAO grading criteria

6. Partially controlled or uncontrolled asthma as per Global Initiative for Asthma (GINA) guidelines in the 4 weeks prior to screening. Participants may be rescreened once asthma is well-controlled

7. Severe asthma as defined by GINA guidelines in the previous 12 months

8. History of emergency visit or hospital admission for asthma in the previous 12 months

9. History of chronic obstructive pulmonary disease

10. History of recurrent acute sinusitis, defined as 2 episodes per year for the last 2 years, all of which required antibiotic treatment

11. History of chronic sinusitis, defined as sinus symptoms lasting greater than 12 weeks that includes 2 or more major factors or 1 major factor and 2 minor factors. Major factors are defined as facial pain or pressure, nasal obstruction or blockage, nasal discharge or purulence or discolored postnasal discharge, purulence in nasal cavity, or impaired or loss of smell. Minor factors are defined as headache, fever, halitosis, fatigue, dental pain, cough, and ear pain, pressure, or fullness

12. History of disease affecting the immune system such as autoimmune disease (e.g., systemic lupus erythematosus), immune complex disease (e.g., serum sickness), or immunodeficiency, which, in the opinion of the site investigator, may pose additional risks from participation in the study, may interfere with the participant's ability to comply with study requirements or may impact the quality or interpretation of the data obtained from the study

13. History of malignancy of any type, excluding basal cell and squamous cell cancers of the skin that only required surgical excision or in situ carcinoma of the cervix study provided that curative therapy was completed at least 12 months prior to informed consent

14. Any of the following:

    1. Inhaled tobacco, vaping, or use of inhaled illicit substances within 6 weeks of screening
    2. Receipt of any investigational product within the past 4 months or 5 half-lives (whichever is longer) prior to screening
    3. Receipt of systemic corticosteroids within 14 days prior to screening
    4. Receipt of immunoglobulin within 5 months of screening
    5. Receipt of other blood product within 30 days of screening
    6. Use of an immunosuppressant or other immunomodulating drug, except for systemic corticosteroids, within 30 days prior to screening
    7. Use of biologics targeting the human immune system within the past 24 months prior to screening
    8. Receipt of any vaccination within the past 6 weeks prior to screening

15. Pregnant, planning a pregnancy during the study, or breast-feeding

16. Bleeding disorders

17. BMI >= 40

18. Other anatomic or musculoskeletal abnormalities that would interfere with FNA sampling procedure

19. History of lymphedema

20. Past or current medical problems or findings from physical examination or laboratory testing that are not listed above, which, in the opinion of the site investigator, may pose additional risks from participation in the study, may interfere with the participant's ability to comply with study requirements or may impact the quality or interpretation of the data obtained from the study